The age of the metal doesn't matter, just if it's rusted away or not. If you're closing the (taillight?) hole, and planning on smoothing it over with bondo, then it probably doesn't matter.
But it it was me, I'd butt weld a patch in.
Thanks.Yeah, it's the taillight. That metal is like 1/32", and I'm afraid if I'm not careful, I'll just start blowin holes
