I am 10 years younger than you ladies and I have the same problem! It may not be age so much as just what your body needs! My thighs scream and my lungs heave for 20 minutes before I can feel comfortable. I just go slow until then. Fortunately my riding partner knows this and is cool with a slow warm up. I think if I were to do a group ride, I would try to ride to the start as slowly as possible to get myself in motion before we took off.