India, Feb. 13 -- The kids are all right. They might just be a little too all right. While most grown-ups spent their 20s and 30s thinking they're invincible (and focused on health only after their first sobering full-body check-up at age 40), 20-somethings today have it determinedly backwards. They're tracking every metric early on, and experimenting with every short-cut that looks promising. Billionaires call it biohacking - the kids do too.

Abhishek Paul, 26, grew up playing sports and following a disciplined fitness routine. It worked until it didn't. Pushing harder no longer showed gains. His gym progress plateaued even as work pressure intensified and burnout crept in. In any other generation, a 20-something would just let go. Paul...