All my life I have been active physically, with varying degrees of intensity. And there's one thing I learned over the years that I thought I'd pass along, in case you find it useful. Life after 40 is not the same as life before 40.
(Yes, I assume I'll have an update in a few years when I hit the big five oh.)
Joints are more sensitive. Muscles hurt longer. Cardio and endurance are great, but speed and rapid twitch muscles not as fast as they used to be. And then there are the special little bits of your body that require extra special attention. Like your sleep.
You need it. Lots of it, if you're going to be training hard. That's true at any age, I suppose, but especially so as you get older. Without my 8 hours, I don't do nearly as well. Also, how you sleep matters more. I have an elaborate pillow system now to cope with various needs my joints have. A special neck pillow, a body pillow for when I turn to the side, and another pillow under my knees to make sure my back is flat on the mattress. It's a very sexy look.
(Raise your hand if you're happy you're out of the dating market.)
Also? Inserts rule. I jog every morning. I aim for 5km daily but sometimes it's more and sometimes it's less, depending on schedule, weather, whether I slept in, etc. I discovered about 15 years ago that I needed strong arch support to avoid pain in my legs. I eventually found a brand and model of running shoes that provided me with the right kind of support. But in recent years, that shoe alone has not been enough; it turns out I also now need inserts.
They work like magic. But then, every few months I start getting pain again in my lower back and hips and stiffness in the knees and all kinds of small ailments. I don't always realize it's the inserts (I'm slow, sometimes, it's almost painful - no, actually, not almost), but eventually I clue in like I did this week and spring for another pair and just like that, the pain is more or less gone.
Generally speaking I don't mind getting older. I like 45-year-old me better than I liked 25-year-old me. But aging forces you to be smarter about how you train, and that's not always an easy thing.