I have posted before and the only bike other than my aluminum cannondale that I have ever rode was my Look KG 96 from 1992.
My son-in-law was a racer and gave me his bike. It is now 25 years old.
How does this frame perform compared with the new CF frames.

What brand/model is the bike. If from a reputable company should be a great bike. Seems to me that the only difference between the older and newer bikes is the weight. Manufacturers have figured out over the years how to make the frames lighter and just as strong. I have an old Look from about 20 years ago. Is still a great bike in my opinion. I prefer and mostly ride steel and Ti bikes, although most of them have carbon forks. Just a matter of preference.

One way to learn is to go try some. form your own Opinion then..

Weight and stiffness. Modern CF frames are lighter and are made to be selectively stiff or compliant according to the area of the frame. An older CF will ride more like an Al frame then what we're used to in terms of current CF frames. In other words, a modern frame will be a tad lighter and more importantly, will deliver a smoother ride with less flexing.

Just watch for cracks or crazing around high stress points. (Head tube connections, bottom bracket, etc.) It should be fine. Carbon fiber assemblies probably never WEAR out. The polymer resin, however, does have a life span. Eventually, it will fail. Exposure to oil, UV, and heat, and maybe salt are all accelerants, depending on the type of polymer used. Two part tube type epoxy from the hardware store, for instance, can start to depolymerize in 5-6 years, and faster with heat. Fiberglass boat hulls last a lot longer, as long as the gel coat that protects them is intact. There are now carbon fiber airplane wings and helicopter rotors, though there is probably nothing as closely inspected, nor as often. It's probably not an issue to worry about, but, at 25 years, you probably want to pay attention to inspection a bit more. Just my $0.02.

The biggest difference is that a CF frame from that era is likely made of lugged carbon tubes- whereas all newer bikes are monocoque, and thus are fine-tuned, by having things like wall thickness and lay-up orientation, etc. customized on every inch of the frame, so that the bike can be stiff where it needs to be; compliant where it needs to be; haevy where it will be stressed; light where it doesn't matter, etc. The old CF bike were essentially built just like any other bike of it's day- only the tubes being held together by the lugs, were made out of CF instead of steel. But if it was a really good racing bike, it's still likely as good or better than half of the bikes out there today- only difference is, today, you could probably get as-good or better of a bike for a lot less money, adjusting for inflation.

No bike is magic. The differences between a mediocre bike and a great bike, are usually quite subtle. If it rides nicely and handles good, you probably wouldn't notice a huge difference going to a good modern bike, even with the drastic changes in technology which have transpired over time.