Is if possible for oil, like gas to go bad if it sits in a boat too long?

I'm getting that '89 Merc 40hp four banger Tuesday. I remembered when I was
talking to the guy that he said it has problems running at top speed. I
asked if he ever ran it without oil in the gas, and he said he always ran a
50:1 mix, IIRC. Well, that boat has an oil injector. Maybe he ran too much
oil. Is it possible to disable the oil pump and run just mixed gas? It
looks like I will have to take some time and a manual on this one to figure
out what's up with the engine, and the tilt. I did pick up fresh plugs for
it.

Should I drain the old oil, as well as the old gas?

Steve