Remember: At our age, we don't heal so fast.
So this leads to a point for you: One of the hardest things to learn is path selection. Get it right, and you will literally expend half the energy of when you get it wrong. If there's one thing you can work on by practice, practice, practice, this is the one I would focus on. If you can consistently take the smooth lines of least resistance, you'll finish better, and less fatigued.
Looking at a rise or descent? Think of mercury on that slope, gravity will help it find the path. This helps a lot. Understanding how to borrow energy to dodge an obstacle (just remember, gotta pay that one back), and making that instinctive, will make a big difference in your day.
Old racer saying: Go slow, to go fast. At our age, we beat the kids because we think our way through, as opposed to gas it and relying upon our youth to recover from the mistakes.
To improve this judgment, is simple. Find a good climb. Sit at the bottom, pick your line. Ride up it, note where and what changed your intended path. Assess. Do the same for the ride back down it. Now read that climb again. Adjust fire. Write the plan, ride the plan. How does reality alter the plan? Adjust. Do it again. Until you've got it figured out.
Then pick a different hill, and do it again.
And again. This isn't out riding with your buddies, this is training, treat it as such. Hell, pick an area where your truck can be close by, get the SO to come and read a book (safety valve in case you dump it bad), and just practice, practice, practice.
You wanna do it safely, and have doing it, then proper prep is the key. The above will also help you train physically too. I used to beat guys because of having thought my way through, not because I had any talent riding. I'm just of average talent, at best. But I had good teachers.