I'm only in my 30s, but it was quite a wake up call, when I noticed my body simply started "failing" in small ways. Knee injury wasn't just a week of "taking it slow", but months, and it's still not really good. If you go to the doctor, you'll suddenly get diagnoses like "yeah, that's how it'll stay now".

The really disturbing thing though is seeing your friends age. That dude who got all the girls in school now has more trenches on his face than Verdun, the super good looking girl now is a woman and becomes a pudgier each year, hair gets gray, skin gets loose. You don't notice that on yourself so much.

And on a social note: the world is shrinking. Those kitchen parties with 30 people you barely know, but met a bunch of new friends are gone. Most of the people you knew in school or university are gone. You try to keep in touch, but that's hard after years of separation. Those who are still close have barely any time left and just hanging out for no reason this evening is no more.

Having a full time job, family and friends simply doesn't work. And that sucks.