I've been managing my wellness since high school. I've worked with weights, ran, cycled, .......... since then. I'm 76 and still do weight work 5 days a week, and ride a lot. My wife was a triathlete and still swims, rides and does weight work 5 days a week. I was a decent distance runner. My wife and I have been bike tourists for decades. When I was 64, my wife and I cycled 3700 miles across the U. S. from Newport, Oregon to Boston, MA in 74 days. Since that time we have spent over 20 months riding over 20,000 miles through 11 different countries. All our trips are self supported, carrying our camping gear. Our training miles are probably close to that. This summer we plan on finishing the last leg of our ride across Canada: Windsor, Ontario to Halifax, Nova Scotia.
My point is: don't talk yourself into getting "older" than you are. However, getting older is a good thing
P.S. I have a friend that finished a 400 km ride last weekend. He finished it with two women, one was 63 and one was 64! That is 248 miles of riding in about 19 hours. He is only in his 50s.