Old lady here. When you're young (teens, twenties), your body can bounce back from all kinds of abuse - eg heavy drinking, extreme sports. As you age, bouncing back is harder, permanent damage can result. Drinking heavily can kill your liver. Extreme sports can kill your joints. Your fifties is when you need to take stock of your general health and do stuff to support it. Like, not furring up/hardening your arteries with bad habits. Exercising so your muscles can support your joints, all that stuff. It's not a time to take up smoking! Soon enough you'll be in your seventies like me, and still striding about enjoying life thanks to the prep you did earlier.

Having said all that, the only area I can think of where I've "let go" is clothing. I dress purely for comfort these days, fuck fashion.