I am no expert either, but I heard that the sound changes for the worse - if you like what you are hearing, I would say don't worry about it. Depending on how the amp was used, it might be still ok - the temperature it was subjected to, and how much it was used.
I have even older stuff I still use without changing caps - 30 years old marantz 2270 receiver, and 20 years old Quad 405-2 amp.