I bought my tail kit in 2001 (I think; it was long ago). The rivets are still working fine on new parts. And the rivets I got with a Mustang II project back in 1990 (they were probably 20 years old when I bought the project) are still good, too.
The sheet metal is either good, or it's not. But age isn't really a factor; just whether it's corroded badly, or beat up due to handling rash over the years.
Welcome back to building, and don't worry about the delays. We all have them. My -7 will fly on Tuesday. That's my story, and I'm sticking with it.