I hadn't mine done at 42. I was bone on bone though, and when they opened my knee up I had plateau parts flying off (little fractures).
I'm a unique case too, I have had lymphoma a for about 15 years and my platelets are shit. So I bled like hell afterwards and didn't heal that well. I was up walking around after 3 days, but I'm a dumbass and tend to rush through anything, wanted to prove I could keep on trucking.
I can't bend my knee fully now, but I can walk and stand now without pain and that's a plus after years of hell. I might have been able to tough it out for maybe a couple more years, but I couldn't stand and put any weight on my right knee at all. Sometimes when I was walking, it would suddenly feel like someone stabbed my knee right in the center with an ice pick and I would go down like a sack of shit.
They last a lot longer than they used to last, and it all depends on how much activity you will be doing, body weight, protoplasm blah blah blah.
Would I do it again? I guess. It was painful for me, the rehab was hard, but I had way more swelling since my blood is that of a shitty vampire now.
Honestly, there were women in the "post op rehab class" right after surgery that were in their 50s to 70s that were kicking around doing nicely. I would be doing the same things but grunting and growning, farting and moaning trying to move since I was a bloody, swollen, sweaty ass mess. Again, judging by what I saw, I would have done well if I wasn't impaired by my inherit condition, so if you are in as much pain as I was where it was keeping me from even doing yard work or going to the gun range, then get it done and go on with it. Take a week off from work, have it done on Monday, then see how you do over the weekend afterwards. That's what I did and was back to work on the following Monday. But, I sit on my ass at home in front of a computer lol.