Fun & Fitness over 50

So anyway, I sign up for this "easy" mountain bike ride and show up at 6PM at the designated meeting place. I'm immediately taken aback. All the riders are young, fit and riding high end bikes. Well there was one other old codger there besides me. I feel a little out of place but hey, I'm a big boy. I can handle it. Besides, it's going to be an "easy" ride.
Not one to hang back, I started right out with the leaders but after a few hundred yards we stopped to wait for the others and I thought better of it. I thought I'd better pace myself a little better and so I let a few more riders go by.
Not much further we stopped again. Word had it that the other old codger broke his chain already. Someone went back to help him fix it but he had turned back and gone home. I think he just bailed cause he realized he was in over his head. Like me, I think he was expecting to see a "healthy" mix of the unfit along with the fit.
There was one other gal there who didn't have much mtb technique but she was obviously young and fit and experienced at road riding. She also had a decent bike.
This was, I think late August or early September and it was hot. Upper 80s and humid.
Mostly I think I did OK. Some of the downhills were a little scary for me and while initially I didn't walk them I did stop at some of the sharper, steeper turns.
I don't know if they didn't say how long the ride was going to be or I just didn't consider it enough but I really didn't pace myself at all. I bit down hard and cleaned all the climbs in the beginning although I probably should have walked some of them. In the end, the ride was just too damn long for me. About 2-1/2 hours in that heat and humidity. I remember on one of the longer climbs midway, I finally lost my breath and my heart was pounding out of my chest and I had to stop before I just passed out. I wish I had my heart monitor then. I could have confirmed my MHR for sure. To their credit, the ride leaders were very responsible and when they saw I was having trouble, had someone behind me and stop with me when I had to recover. One guy was always signing to me to drink. I feel bad to think back on it. They must have thought me a grouch cause I didn't answer anyone most of the time when spoken to but I was just so utterly exhausted I literally couldn't speak. Also, it was getting late and i was concerned about getting out of the woods before dark. I got so tired at the end that I just couldn't handle even downhills that I could have handled in the beginning. I just walked down, straddling the bike. All attempts at saving face gone. I felt totally humiliated but too tired to care about anything but getting out of the woods. Finally we did. I made it.
I kind of joked in the last post about this being an "educational" ride and I call it a "death" ride but it really was a seminal experience for me. For one thing, I resolved to never ride a group ride like that again until I was physically ready and had a better bike. I also realized I could ride a lot harder than I had been training and not die. And I resolved that I would go back and train myself harder and more consistently and one day be able to finish that ride respectably. Actually I was proud that I finished the ride on my own power and didn't quit. (What was I going to do? Sit down and demand that they carry me out of the woods on a litter?)
I have been training harder and more consistently but I don't feel ready for another "easy" ride. I would like to do some true beginner rides and join some road rides at touring speed. This will happen this year.