Can't outrun youngsters now but my Back has recovered!
I'm only 5 10 . To get some speed, I tried that trick where you raise your seat so high that you are on tippy toes when you are at a stop. I think I bumped it up 2 and a half inches.
It worked for me and for a while last summer I could ride with the youngsters. I think it's because you use your upper leg muscles more strategically.
Unfortunately riding with my seat that high brought on terrible back pain by fall and back pain is worse than knee pain or arm pain or even a migraine. It echoes through your body.
I tried to deny it , but in the end common sense prevailed. I lowered my seat by several inches last month .I feel great now.
I'm slower, but who cares?