[thenomad]

I've had a similar experience. I gave up working late around 30, when I found it wiped me out too much. Now I'm 36 and I've discovered I can do 12-hour days again.

Why? Better diet (Paleo) and daily exercise. Bodyweight and Pilates, in my case, but I'm planning to try powerlifting at some point. (I remain convinced that mind-body exercise like T'ai Chi, Pilates or yoga are one of the best body hacks out there. )

For some additional "Old Guy" inspiration, here's Joe Pilates, the inventor of Pilates, at 51 and 82. He, erm, doesn't exactly look it: http://www.vivianzapanta.com/look-at-joseph-pilates-age-51-a...