In May of 2013, the DOT came out with a new requirement for labeling the back of helmets that are approved for motorcycle use on public roads. I doubt there's much interest in used helmets that are older than 2013 for actual road use, although there is such a thing as helmet collecting.
A helmet has some components in it that degrade with age-- foam, vinyl, nylon, polyester, leather. Almost everything gets weaker with age.
A helmet has some components in it that degrade with age-- foam, vinyl, nylon, polyester, leather. Almost everything gets weaker with age.