I'm in the process of getting a set of Cargar S/S wheels, 2 are 15x8, 2 are 15x7, off of a mid-year Vette. The owner decided he wanted a new set.

Is there a way to tell how old these wheels are?

I was told that they are about 30 years old, but I have no clue as to how you date these wheels, if there is one.
Any ideas?
Thanks, Andy