My hair-thinning had gotten really bad, plus a wealth of other health issues. It was only when I realized that I had been taking high-dosed tranquilizers every day, starting in the morning, that I could admit to myself that I had a stress problem. On top of my objectively ridiculous workload, I started interviewing, and it took a long, very painful year to find a new job that was better in every way. And wouldn't you know, within a year, my hair grew back so thick that I could hardly run a comb through it even when it was short and wet. It took a few more years for most of my other, stress-related issues to abate, though.
And to counteract some of the negativity in this thread, some people positively don't seem to age, especially those regularly working out. I've known men and women that looked exactly the same over 20, even 30 years.
TLDR: Work out for fun, and don't ever get salaried.

I'm 43 and the thinning hair the only real indication so far. I stretch, and lift weights so that I can stay fit enough to surf, and I ride my Ebike everywhere that I can. As long as you stay active, you don't really feel it till your 70s or 80s. Eat your veggies kids. You can't outrun your diet.

I have had constant physical pain since my 20s, and had to to accept being bald before I turned 30.

Speed running life, basically.