As a full time auto tech I will agree with everything said so far. With proper maintenance engine can run many thousands of hours. There us no cut and dry way like hrs to tell if a motor needs rebuilt. But there are a few basic and easy check with tools that don't cost much or are rentable through the local parts store.

One i like to start with that gets overlooked alot is a simple vaccum reading. Given the overlap in the cam grind of most marine motors reading around the 13 area are not uncommon. The more the overlap in the cam the less and more erratic that number becomes. But you want to see a fairly steady reading, you don't want to see very very rapid jerking or bouncing of the needle.

Do a compression and cylinder leak down or balance test. On the compression you are looking for even readings would guess 150 psi plus seeing the hrs you have. I like the leakage test better, over 20% is bad, seeing you ours 10 to low teens would be normal.

As far as bottom end we only have oil pressure and I have seen motor with 50 psi knock and motors with 10 psi run perfect. You can cut open your old oil filter check for fine metal powder, thst would indicate an issue

Motors can go bad at any time I have seem them with less than 100 burn up. Keep in mind there are hundreds of moving parts often times with 2 or 3 thousandths of inch of clearance and a small film of oil, running at 3000 plus rpms sometimes hours at a time. And these are built by a company that is looking to save a penny at any chance they can.