How old is too old for a hitch

It is probably ok but if it were me, I would replace it. There have been a lot of improvements in both technology and variety in WD hitches since 1993 and you also don't know about any metal fatigue that may be present.
Barney

Twenty-five year old equipment with that much weight and importance....replace!

I have a solid Reese WD hitch head that is of similar age. It's still going strong.

Steel, to my knowledge, does not fatigue. At least not within the limits relevant here.

I would rock it indefinitely. My WD bars are newer than that but the hitch head itself is doing fine.

I've had to replace a hitch head due to egged out load bar sockets but still use it for dead weight pulls without weight distribution. I've also replaced hitch balls due to wear and slop. I don't think you really age out this equipment but it does wear or corrode over time based on use.