As above really.
I'm using a 1996 Trek 1400 (made of Easton Program alloy, if that matters) & matching alloy forks that I picked up a few months ago - it's a lovely bike and rides really well, but I've never had an alloy frame before and I'm a bit concerned about longevity, specially as I've no idea what's happened to it in the preceding 13 years.
Anyone still happily using an alloy frame of this age?
I think (though please, anybody correct me if I'm wrong) that the program aluminium frames were not meant to be welded, but bonded with adhesive.
This may throw up different issues, or not, compared with the normal problems of alloy frames.
I do know of bonded Treks from that era that are still used everyday as workhorses, so I'd just enjoy using it, but keep an eye out for any prob's.
I use a 20 year old cannondale M800 (welded alu frame) with no problems or concerns
see that piece of string....
Impossible to say, even if you knew the history it would be difficult.
Ride it but keep an eye and ear out for anything that changes.