I've always read that average boat use is about 75 hrs per year. But typically that varies if you live in a warmer or cooler climate. And if your messing with boats where people are passionate about getting out a lot (like wakeboard boats).
My previous boat was an MC 205, purchased when it was 5 yrs old with only 60 hrs on it. The engine & drivetrain never had a single bit of trouble. I did tune the engine up, and replace the belts & hoses & the impeller. But those are things you should at least inspect on any used boat purchase, if not replace anyway.