HOW SAFE IS RUNNING AT AGE 50 ON TREADMIL,4-5 TIMES AWEEK FOR 30
MINUTES.WEIGHT 92KILOS, HEIGHT 176 CM.GENERAL HEALTH IS GOOD EXCEPT
HIGH CHOLESTEROL

Nothing is completely safe, but my guess is low risk if you stop or
slow before you reach exhaustion. 30 minutes is likely too long for
the first few times. You need to work up to it gradually.   Neil

Dont run too fast, because your heart wouldn't take it at this high rate of pulse. 
To be a little on the side track: Arnold Schwarzenegger even in one of
his comments said that he stopped exercising because he is over 50. I
am not saying that taking the celebrity words is of any importance.
But from my personal knowledge and visits to doctor about my parents
have taught me that too strenous work at the age of 50 is not
recommended but walking at high speed is okay. Instead of running for
an half hour, walk for an hour.