How Old is Old when considering an Amp? Krell, Bry

Greetings folks. I posted earlier in the week about wanting upgrading my system with a more musical and powerful amp. Heard a Krell system a few years back and really dug it!!! Came accross this KSA 150 and thought it looked inticing. It is my understanding that this unit could have been manufactured from 91-94 ish? How old is this in Class A Amp. years? Is there a point where all good amps must reasonably perish?

Also am curious about any used amp in the 1.5 - 2k range. How's Classe CA 200, Bryston, Plinius? Don't know much about high-end yet but am anxious to learn.

current system:
power plant: PS Audio PS-600
pre-amp: Audio Research LS3
cd: Naim CD5i
amp: Rotel RB 981 {120 wpc} weakest link!
speakers: Paradigm Studio 100's V3.
speaker cables: Transparent "The Wave"
interconnects: Interlink "The Link" 200