If it matters, I am 69, race road and track and had 10 race days this season. We are all different so a one size fits all answer typically does not work. I always prefer a slow warmup with ever increasing force and then some efforts to match what efforts are planned for that day. Hence preparing the bodies systems of ATP-PC, glycolytic and aerobic. However, that can be done in 20 minutes plus minus.

I suggest being careful of what “feels” good. Many times my legs do not feel great but they are ready. The problem is that if one keeps warming up until they feel perfect, one may pick up a lot of fatigue that will be detrimental to the planned activity. Warmup is NOT an effort!!!!

So try going harder on your ride to start of the group ride and see if it helps. I suspect it is conditioning. You need more juice in your legs. Sorry. More threshold and VO2 solo work. Also, do not play the age card. It will not do you any good and it gives your brain an excuse for non performance. When my legs feel bad, I tell my brain that is the way they are supposed to feel. Get over it. Jens V just tells his to shut up.

The good news for you is that they feel better over time and you have power at the end or at least you think you do. The entire group may be slowing down or the wind / terrain has changed.

Also, I never feel compelled to do “my fair share” of a pull. If my legs are not great, I take a couple of pedal strokes and rotate out. There is no money or anything else handed out at the end of a group ride to the valedictorian of the group ride. Having said that, I suggest challenging yourself since that is one of the reasons you are on the ride.

My opinion is that you lack 5 minute power. Work on that between group rides and I suspect you will feel a lot better at the start and finish. Good luck.