If you think 50 or 55 is old, what does that leave for those who are 70+ or even over 80? The Sunday run/breakfast group I joined in 1971 now has 13 members over 80. (I do not count the 5 or 6 who have passed on.)
Our group still meets to run, jog or run, whatever each can do, every Sunday morning before we have breakfast together. Outlook can make a big difference in aging.