Hello bluekat
Here is the US data for causes of death in males, in 2000, according
to age. However, the highest age group given is 65+
The data are from the National Center for Injury Prevention and
Control
web site, and you can select reports for 1999 onwards or for 1998 and
before on this page: http://webapp.cdc.gov/sasweb/ncipc/leadcaus.html
Selecting 1999 onwards brings you to another page where currently the
choices are only for 1999 and 2000 data. You can select various
display options. I've selected age groups as you requested and the top
10 causes of death for each group (you can select up to 20 causes).
The results can be downloaded in spreadsheet format (csv)
10 Leading Causes of Death, 
2000, All Races, Males
Age
Group    Rank   Deaths    Cause of Death
<1 
         1        3,028   Congenital Anomalies [birth defects]
         2        2,391   Short Gestation
         3        1,509   SIDS [sudden infant death syndrome]
         4         791    Maternal Pregnancy Complications
         5         643    Respiratory Distress
         6         569    Placenta  Cord Membranes
         7         501    Unintentional Injury 
         8         447    Bacterial Sepsis
         9         357    Circulatory System Disease
         10        352    Intrauterine Hypoxia
1-4 
         1        1,098   Unintentional Injury 
         2         259    Congenital Anomalies
         3         233    Malignant Neoplasms [cancer]
         4         198    Homicide 
         5         107    Heart Disease
         6         54     Influenza & Pneumonia
         7         53     Septicemia
         8         52     Perinatal Period
         9         33     Benign Neoplasms [non-cancerous tumors]
         10        28     Chronic Low. Respiratory Disease
5-9 
         1         824    Unintentional Injury 
         2         269    Malignant Neoplasms
         3         105    Congenital Anomalies
         4         77     Homicide 
         5         64     Heart Disease
         6         32     Benign Neoplasms
         7         27     Influenza & Pneumonia
         8         26     Chronic Low. Respiratory Disease
         9         24     Septicemia
         10        17     Anemias
10-14 
         1        1,037   Unintentional Injury 
         2         300    Malignant Neoplasms
         3         238    Suicide 
         4         150    Homicide 
         5         102    Congenital Anomalies
         6         99     Heart Disease
         7         54     Chronic Low. Respiratory Disease
         8         21     Cerebrovascular [stroke]
         9         21     Influenza & Pneumonia
         10        17     Benign Neoplasms
15-24 
         1       10,460   Unintentional Injury 
         2        4,203   Homicide 
         3        3,424   Suicide 
         4        1,022   Malignant Neoplasms
         5         638    Heart Disease
         6         268    Congenital Anomalies
         7         120    Chronic Low. Respiratory Disease
         8         106    Cerebrovascular
         9         102    Influenza & Pneumonia
         10        99     HIV
25-34 
         1        9,059   Unintentional Injury 
         2        3,938   Suicide 
         3        3,361   Homicide 
         4        1,922   Heart Disease
         5        1,854   Malignant Neoplasms
         6        1,602   HIV
         7         376    Diabetes Mellitus
         8         308    Cerebrovascular
         9         280    Liver Disease
         10        279    Congenital Anomalies
35-44 
         1       11,444   Unintentional Injury 
         2        9,286   Heart Disease
         3        7,344   Malignant Neoplasms
         4        5,114   Suicide 
         5        4,441   HIV
         6        2,319   Homicide 
         7        2,314   Liver Disease
         8        1,297   Cerebrovascular
         9        1,151   Diabetes Mellitus
         10        630    Influenza & Pneumonia
45-54 
         1       25,927   Heart Disease
         2       24,215   Malignant Neoplasms
         3        9,063   Unintentional Injury 
         4        4,975   Liver Disease
         5        4,149   Suicide 
         6        3,296   HIV
         7        3,235   Cerebrovascular
         8        2,821   Diabetes Mellitus
         9        1,661   Chronic Low. Respiratory Disease
         10       1,425   Viral Hepatitis
55-64 
         1       48,427   Malignant Neoplasms
         2       43,285   Heart Disease
         3        5,564   Chronic Low. Respiratory Disease
         4        5,496   Cerebrovascular
         5        5,133   Unintentional Injury 
         6        4,943   Diabetes Mellitus
         7        4,005   Liver Disease
         8        2,265   Suicide 
         9        1,680   Influenza & Pneumonia
         10       1,651   Nephritis
65-74 
         1       83,191   Malignant Neoplasms
         2       74,589   Heart Disease
         3       16,210   Chronic Low. Respiratory Disease
         4       12,042   Cerebrovascular
         5        8,226   Diabetes Mellitus
         6        4,639   Unintentional Injury 
         7        4,013   Influenza & Pneumonia
         8        3,564   Nephritis
         9        3,317   Liver Disease
         10       2,867   Septicemia
75-84 
         1       109,693  Heart Disease
         2       85,907   Malignant Neoplasms
         3       23,946   Cerebrovascular
         4       23,838   Chronic Low. Respiratory Disease
         5        9,751   Influenza & Pneumonia
         6        9,738   Diabetes Mellitus
         7        6,228   Alzheimer's Disease
         8        6,213   Nephritis
         9        6,063   Unintentional Injury 
         10       4,530   Parkinson's Disease
85+ 
         1       78,896   Heart Disease
         2       33,260   Malignant Neoplasms
         3       18,212   Cerebrovascular
         4       11,876   Chronic Low. Respiratory Disease
         5       10,945   Influenza & Pneumonia
         6        6,406   Alzheimer's Disease
         7        4,671   Nephritis
         8        4,413   Unintentional Injury 
         9        4,234   Diabetes Mellitus
         10       3,387   Pneumonitis
The UK statistics are available from National Statistics
http://www.statistics.gov.uk/default.asp
The actual file you want is available in Excel or csv format at 
http://www.statistics.gov.uk/STATBASE/ssdataset.asp?vlnk=6879
It includes separate data for males and females.  The figures are not
presented as clearly, so I have tried to sort them out for you.  Also,
the age ranges are presented in 10-year blocks from age 5 upwards and
in the lowest age group do not include deaths occurring at under 28
days of age.
Age
Group    Rank   Deaths    Cause of Death
<1     
          1      129      Complications just before or after birth
          2      115      Congenital diseases
          3       96      SIDS
          4       52      Diseases of nervous system
          5       20      Pneumonia
          6       19      Heart disease
          7       18      Digestive system diseases (not liver)
          8       16      Accidents
          9       13      Septicemia
         10       12      Assault
1-4      
          1       50      Accidents
          2       49      Congenital disease
          3       46      Cancer
          4       37      Diseases of nervous system
          5       22      Hormonal, nutritional and metabolic diseases
(various)
          6       17      Meningococcal infection (bacterial
meningitis)
          7       13      Heart disease
          8       11      Septicemia
          9       10      Assault
         10        7      Digestive system (not liver)
5-14      
          1      123      Cancer
          2      121      Accidents
          3       64      Diseases of nervous system
          4       34      Congenital disease
          5       24      Hormonal, nutritional and metabolic diseses
          6       13      Heart disease
          7=       9      Assault
          7=       9      Digestive system (not liver)
          9        8      Cerebrovascular
         10=       7      Benign neoplasms
         10=       7      Blood diseases
         10=       7      Pneumonia
15-24      
           1      881     Accidents
           2      373     Intentional injury
           3      185     Cancer
           4      167     Drug abuse
           5      127     Diseases of nervous system
           6       60     Heart disease
           7       46     Hormonal, nutritional and metabolic diseses
           8       41     Congenital disease
           9       22     Digestive system (not liver)
          10       19     Cerebrovascular
          
25-34      
           1      901     Accidents
           2      799     Intentional injury
           3      359     Drug abuse
           4      338     Cancer
           5      300     Heart disease
           6      155     Nervous system
           7      120     Liver disease 
           8       60     Cerebrovascular
           9       55     Congenital disease 
          10       41     Pneumonia
35-44 
           1      1464    Heart disease
           2      1081    Cancer
           3       864    Intentional injury
           4       793    Accidents
           5       580    Liver disease
           6       258   Nervous system
           7       218    Drug abuse
           8       126   Pneumonia
           9       123  Assault
         10         58   Congenital malformations
45-54 
         1       4823    Heart disease
         2       3960    Cancer
         3       1068     Liver disease
         4        640    Accidents
         5        639    Intentional injury
         6        598   Cerebrovascular
         7        389   Nervous system
         8        260   Pneumonia
         9        149   Drug  abuse
        10        129   Diabetes mellitus 
NB from this age up, diabetes mellitus forms the greatest proportion
of hormonal, nutritional and metabolic disease, while previously it
was negligible.
55-64
       1        11,220     Heart disease
       2        11,124     Cancer
       3          1387     Cerebrovascular
       4           980      Liver disease
       5           941      Chronic respiratory
       6           690      Digestive system (not liver)
       7           552     Nervous system 
(of which motor neurone disease = 148)
       8           505      Pneumonia
       9           478     Accidents
       10          430    Aortic aneurysm
    
65-74
        1     23,141   Heart disese
        2     20,776   Cancer
        3       4065    Cerebrovascular  
        4       3191    Chronic respiratory
        5       1526    Aortic aneurysm
        6       1515     Digestive system (not liver)   
        7       1199   Nervous system 
(of which 355 = Parkinson's, 282 = motor neuron, 204 = Alzheimer's)
        8       730    Diabetes mellitus
        9       699    Liver
       10       554   Accidents
75-84
      1     34,777   Heart disease
      2     24,166     Cancer
      3       9261     Cerebrovascular
      4       6072     Chronic respiratory
      5       4420     Pneumonia
      6       2719     Digestive system (not liver)   
      7       2490   Nervous system 
(of which 1193= Parkinson's, 201= motor neuron, 689= Alzheimer's)
      8       2428    Aortic aneurysm
      8       1476    Vascular and unspecified dementia
      9       1408    Genitourinary disease
     10       1052     Diabetes   
85+
      1     18,289    Heart disease
      2      9422     Cancer
      3      6954     Cerebrovascular
      4      5690     Pneumonia
      5      2858     Chronic respiratory
      6      1781     Vascular and unspecified dementia
      7      1758      Senility without psychosis
      8      1477     Nervous system 
(of which 689 = Parkinson's, 554 = Alzheimer's)
      9      1374    Genitourinary disease
     10       970    Aortic aneurysm |