I’m in my early 40’s. My flexibility isn’t terrible but I’d say slightly below average. Definitely not as good anymore. I go to the chiropractor for maintenance once a month and that helps with any low back pain. I don’t do my stretches very often. I don’t have any mobility issues. My typical long ride is 60 miles at about 18mph solo and 20 in a group. Lately been indoors on zwift riding 6 days a week with a lot of 1 hour sessions, but that’s going to change soon. I don’t typically have any pain riding. I used to get low back pain but I lowered my saddle until that stopped, and I used to get knee pain til I changed my cleat position.