At 73 I get about 10 miles than have to stop and stretch for a minute due to pain in the knees. After a couple of toe touches I'm good to go for the rest of the day with little to no pain. Didn't need to stretch at all until I was in my late 60's. Everyone is different. Hopefully your's is nothing serious either. Get it checked out for peace of mind or find what works for you. Good luck,