38 is around the age where your body starts giving you subtle hints that you aren't as young as you think you are and then at 40 it starts sending you the messages a little more aggressively.
Doesn't mean you can't still do most of the things you want, it just means that you have to spend more time recovering and doing things to minimize the messages it sends.
I'm heading towards my late 40s and still work my ass off training and probably am in the best combination of jacked/lean in my life but I definitely have to put a lot more time into recovery, sleeping properly, nutrition and ensuring I don't injure myself during my workouts than I ever have before, and still am usually dealing with some sort of nagging pull/tight spot, knot, etc.
It's just part of aging...perhaps you are starting to feel that a little more now, which means you are in tune with your body which means you will be able to do a lot more than most at working around and preventing the worst of it.