At what age does a person start to get old? i'm not talking about feeling old. i mean getting old by the age number. i know about young as feel.

Depends . . .: In the states, typical retirement as well as qualification for medicare (aside from disability) is 65yo. As a geriatrician, we consider 65-75yo as young old, 75-85yo as middle old, and 85+yo as old old. Of course you could always argue by semantics that you get older each day after you're born. But i think you're looking for 65yo as when you get "old" numerically.