I thought this thread might get into my problem- my legs just get really tired and hurt ON the bike, and I can't seem to keep up with people because it hurts.

A few random thoughts...
I haven't ever tried the compression tights... maybe it's worth a try because sometimes I do have a lingering soreness for more than a day. I'm 56. I rode 75 miles Saturday and Sunday did not want to get on the bike at all but was ready to ride Monday. After my first century last year (actually 111 miles) I did an easy recovery ride on a flat MUP trail, and I think it was very helpful.