Man, me too. I'm 55 now, so I'm much better at it - finally. 6-8 years ago I was working out with a world class trainer (a guy named Bennie Wylie) and a bunch of 20-30 year olds every day. My competitive juices were flowing. I was outworking most of them, but I was getting injuries and aches constantly. At 50 I finally decided that I was being really stupid. There's a reason pro athletes retire in their 30s or maybe early 40s if they're REALLY lucky. I finally decided that I am exercising to be healthy and feel better, not worse. So I quit working out with that group. It was just too hard to be with them and take it easy. I've been feeling much better ever since.
Bennie left Abilene and got back into being a college football strength coach at OU. He's at USC now. He's a freaking beast. Great motivator and trainer too. I wish I was young enough to keep up with him.