PA used to be 25 years, but when they tightened up emissions a while back they lossened up the classic definition to 15 years. In PA classic tags don't require emissions testing, but you're use is supposed to be limited to 1 day a week and/or parades, club events, tours, etc. Basically a bunch of non-enforceable BS.
For my next stunt I'm going to register my '95 Hardbody as a "farm vehicle".