I think there is no such thing as a old thread to an oldster.

It may be a geo-cultural thing, around here they are plenty of guys in their 60s riding 'racing' bikes, modern and vintage. Healthy drops between the saddles and bars. Many are wearing skin tight racing kits as well, and that may be where you might wish to draw the line...most old bodies ain't looking very svelte in skin tight clothes, yo.