I agree -- pain and suffering are complex and different for different people at different times in their lives. I also agree that pain and suffereing are pretty central parts of the human condition, witness its treatment by different religions. Its common for people to want to avoid pain. In some ways that's natural and healthy; in others, not so much.
One of the positive pain lessons of budo or athletics generally, and especially for the young, I've called in the past "learning how to suffer."
That's a different thing from an "I'm being injured" signal, although I'm not always successful in distinguishing between the two, and its hard sometimes, especially in the middle of rigorous practice, for me to tell the difference.
In the last few years, as I've grown older, I've accumulated some permanent damage to my body. If you want to suggest to me that damage reflects mistakes I've made, I'd readily agree. But it seems kind of irrelevant at this point, and, anyway, some of that damage is just the after-effect of what I consider a life well-lived. Trying to preserve a pain-free existence as you grow older seems frankly delusional and self-limiting. Cf. Buddhism generally.
In any event, lately I think I have begun to become acquainted with a different kind of pain, which I also think relates to what Mary was addressing.
I feel like for me to do what I still want to do -- say, participate fully in a multiple-day seminar, or mix my aikido practice with other activities that I love, there's a price to be paid. Not only that, I know it will take time to recover from the debt. It's just a question of whether I want to put up with the terms of the bargain I'm making with myself.
I'm coming to think of it as "old-guy endurance."
Choosing to endure this discomfort feels different. It requires me to struggle more with the psychological urge to just stop. As Paul Simon wrote in a song, I sometimes think "I don't find this stuff amusing anymore."
It also feels like a taste of what older people face every day doing even simple things, and it feels like it takes a different and deeper kind of courage to face. It's something, frankly, I still need to learn.