I am 51, and while whittierider's words, give me comfort, I am not there yet.
Up until I turned 40, I used to be able to hang with the college kids and leave many of them doubled over and puking. Since then, age has taunted me. I have some knee pain that seems controllable as long as a pedal at a good cadence. I had saddle issues that went away once I switched over to leather saddles. I have recently had prostrate issues, but a leather saddle with a cut-out, and proper fit seems to be the answer to prostrate issues.
The biggest challenge seems to be keeping balance in my life.
I spent my 30's as a divorced guy, so there were many biking adventures. I did some pretty cool stuff. Toured Cape Breton and part of the Continental Divide. Rode the length of the Keweenau Peninsula, and up one of Michigan's coasts and down the other. Learned to Eskimo roll a kayak. Stuff that none of my peers did.
I remarried at at 42, and lets just say that being married is time consuming. My new bride knew about, but was not prepared for all the time spent paddling and pedaling. In the end, I kept the wife, kept the bikes, and scaled back the boats. Last year I sold my fancy British touring kayak to pay for my new custom touring bike. My riding partners also married, and it seemed we spent a lot less time riding together.
When I entered the work force as a novice engineer in 1981, engineers were treated as a treasured resource. This decade is lot more different. We are up against the pressure to can us and ship the work to India. We are up against the pressure to replace us with younger workers. Never mind that I don't choke under pressure and the youngsters do. I have a hard time finding enough time to ride like I used to.
The good news is that I picked up someone new to ride with. In the beginning I mentored him along; now I relate to Victor Frakenstein. If it is above 25F, John drags my sorry butt out for a ride. You riders from Southern California or Florida probably have never ridden on iced road after dark, but this is how I spent my winter this year. We will see if I can swing carbide tipped studded tires for next winter.
Also on the good new front is that riding is still the spiritual experience it always was. I always return home with more than I left with. I still tour, I just have to find something I can do in less than a week. And I am still doing stuff that none of my peers do.
I guess that I hold out for my retirement years. I have this expectation that I will have enough time then to ride all I want. That I will have trained enough that I can ride like I did as 30-something. That the absence of stress will make weight management easy like it used to be.
I am OK with slower acceleration--I just want to climb like a billy goat again.