Great question, great answers. For me music is a tonic. Last year I had major surgery and I spent months recuperating at home. I spent my time doing three things for the most part- listening to my music, watching James Bond movies, and sleeping the day away on pain meds (well, that was especially the case the 1st month). I also found renewed interest in my system through that time. I had been working so hard up to then I sort of neglected listening to music. In the 1 yr plus since my operation I have 1- changed my digital source; 2- had my tuner upgraded; 3- changed interconnect cables; 4- changed speaker cables; and 5- changed integrated amps. I also had my turntable tuned up; the only thing I didn't change were speakers and my phono preamp. And with my speakers, once I could actually move them around (I had a weight limit of how much I could manipulate; heck, I found it hard to open the fridge door at first)I used the Cardas placement program to reposition my speakers (it worked out well).
So my answer is this- as long as I am healthy and can still get enjoyment out of my music, and the funds allow, I don't see that there really is any age at which to buy one's last amp.