Why do some people change so much in their appearance from youth to old age and others do not?

Why do some people change so much in their appearance from youth to old age
and others do not?

I see photos of those I knew in my youth and if I met them in
person now I wouldn't recognize them.

I have ran into people I knew 40 years ago and they say I
haven't changed.  Why?

4-14-2020