Use it or lose it. I'm over 40 and yesterday suited up for a house fire. I'm still weightlifting a few times a week, along with running, gardening, and nightly walks. I generally don't get pain really anywhere unless it's from overtraining.

Obviously you can overdo it, I've injured my back a few times trying to hit a risky lift or pushing too much. As I'm getting older I'm seeing the value in moderation. Still lifting, just not trying to push myself too hard.

I was lucky, when I was really young I hurt my back pretty bad, and had to start lifting to heal it. Just realized early that lifting reduced my back pain, so I built to the habit. Any time I get lazy and stop within a few months I'll get back pain again. So I keep it up.