The only reason age of the overhaul should matter is if it was sitting for all that time... and even then it may start up and run just fine till TBO. The issue is if internal parts... mainly the cam/crank bearings but also other things have rusted and pitted? That can happen in a couple months in the wrong conditions or not happen for years in the right conditions.
If the airplane was flown often enough the parts would have been re-coated in oil and any moisture boiled off each flight. That's probably the only thing you can really use as an indicator... whether or not it was flown continually.
My airplane, an Archer II, has an engine rebuilt in 2001. When I bought it, it had been sitting for almost a year. My only issue in some 250-ish hours and 3 years in it has been a magneto failure on the ground. Good compression, normal oil consumption, good power. I wouldn't be afraid to buy another in the same condition and fly it based on my experience. I'm not afraid to take my airplane anywhere I'd feel safe taking a brand new one either.
Cliff notes: Age of overhaul isn't a huge deal, just check the overall condition/compressions/etc and don't worry too much about it.