Hopefully this helps someone else. I'm approaching 50. I just took up mountain biking after moving to an area that has lots of trails. I have seen gains in my health and my mood that I worried might not return. I ride with a guy who's 60 and he regularly smokes the rest of us. My wife and I started kayaking together recently and that's done wonders for mood, health, and our marriage. So, here's my advice:

1) Don't stress about your age. And don't stress about approaching an age. Enjoy whatever age you are. Instead, consider your condition. Should you improve it? Can you improve it?

2) To help with #1, find a hobby that gets your heart rate up and uses a good portion of your body. Better yet, find multiple hobbies that exercise different areas of your body.

3) For me, the key to #2 was finding a hobby that actively engages my mind at the same time. I needed the rush and challenge of riding on trails that mountain biking offers. But for kayaking, I thrive on the opposite. The tranquility of the water and being out on a date with my wife is a sort of meditation. In both hobbies, I come home refreshed and energized. If you haven't found such a hobby yet, keep trying different things until something clicks. You'll probably know it when you get there.