I've been lurking on the classic forums for several years. Why? Because I am not a collector, or a restorer, or a perfectionist, or an expert. I am however a rider. I ride old steel frankenbikes, all double or triple butted. If they need painting, I paint them, with a brush. If they need new or adjusted fittings I silver braze them because I don't have a torch hot enough for brass.
I will turn 76 this month. I am still riding the bikes that I rode in triathlons, including Ironmans, during the last 33 years. Admittedly they all have triple cranks now. This year I have done two 75 km rides, two 100 km rides and one 140 km ride and numerous shorter rides.
How you ask? Because 40 years ago, after an unwise heavy lift, a physiotherapist told me I now had scar tissue in my back and would need to do daily stretching for the rest of my life or suffer more torn tissue and subsequent pain. It only took 3 recurrences to convince me. Moral of the story, work on flexibility. When a new problem crops up go to a physiotherapist or GO ONLINE and find the stretches that will work to fix the problem. If they cause sharp pain when you start then ease into them gradually. Your body will respond. These days I'm doing daily stretches for my lower back, hips, knees, plantar facia (feet), arms, shoulders (swimming), and neck. Takes about 1/2 hour and gives me not only immediate relief but I'm still riding the drops and am more flexible than any of the people I ride with all of whom are younger than me.
I won't lie, I'm significantly slower than I was in my 30's and 40's but I'm still having fun and that's good enough for me.
Cheers, and good luck.