what is yhe normal age for kids to start talking? my son is going to
be 3 at may and still didnt talk

Dear Aziz, 

First of all, don't take this answer as a professional advice given by
a developmental psychologist or a pediatrician, see Google Answers'
disclaimer on the subject:
"Answers and comments provided on Google Answers are general
information, and are not intended to substitute for informed
professional medical, psychiatric, psychological, tax, legal,
investment, accounting, or other professional advice."

However, if your child is already two-and-a-half years old and isn't
talking yet, it might be a source of concern, and I urge you to see a
doctor as soon as possible: children are supposed to be able to say a
few words by the age of one, and by now he was supposed to already
compose short sentences:

"25 to 36 months
Your toddler may struggle for a while to find the appropriate volume
to use when talking, but he'll learn soon enough. He's also starting
to get the hang of pronouns, such as "I," "me," and "you." Between
ages 2 and 3, your child's vocabulary will grow to up to 300 words.
He'll string nouns and verbs together to form complete, simple
sentences, such as "I go now."

By the time he turns 3, your child will be a pretty sophisticated
talker. He'll be able to carry on a sustained conversation and adjust
his tone, speech patterns, and vocabulary to his conversation partner.
For instance, he'll use simpler words with a peer, but be more verbal
with you. By now he may be almost completely intelligible. He'll even
be a pro at saying his name and age, and will proudly oblige when
asked."
(SOURCE: Paul Young, M.D., "Developmental milestones: Talking", Baby
Center, July 2005, <http://www.babycenter.com/refcap/baby/babydevelopment/6573.html>).

I cannot say if there is a problem, or that the situation is not that
dim - a friend of mine hadn't spoken until he was almost four, but
then he made complete sentences. He is now a mathematician, a very
clever fellow by all means, and... he wouldn't stop talking :-)

However, it is important to get these things checked as soon as
possible, because it is possible that your child has a speech
development problem. Read more about it here:
Jennifer Newton Reents, "Early Intervention Key in Language
Development", Toddlers Today,
<http://toddlerstoday.com/resources/articles/langdev.htm>.

Read more: 
When should my baby start talking? (August 2000), from: Keep Kids Healthy
<http://www.keepkidshealthy.com/development/language.html> 

Literacy Trust - Supporting early language development and communication skills 
<http://www.literacytrust.org.uk/talktoyourbaby/resourcesprof_earlylang.html>
- links to articles about speech development.

Caroline Bowen, 1998. "Speech and Language Development IN INFANTS AND
YOUNG CHILDREN" <http://members.tripod.com/Caroline_Bowen/devel1.htm>

I hope this answers your question. Please contact me if you need any
clarification on this answer before you rate it. My search terms:
child development speech, child development "start talking"

By memory, I think Einstein didn't talk until he was much older than
that, but don't count on a late talker being Eintein.

Aziz,
If you are raising your child in a bilingual home, I have heard that
in some cases that may delay talking.  You should also consider having
his hearing checked by a specialist who deals with very young
children.
Of course, I am also no professional.
Best wishes, Myoarin

Out of personal experience, please take your child to a developmentl
pediatriican ASAP if your child is not talking by 3.  Einstein and
bi-lingual home environments are not suitable explinations for your
situation.  If it is nothing, then no harm can come from a quick
visit, but if there is a porblem, the sooner you address it, the
better for the child.