IMO the function of an hour meter is to schedule maintenance on properly and regularly run engines. So, as others have said, it comes down to care and operation of the engine, not numbers on the hour meter. Get a survey by a mechanic familiar with the engine(s) in the boat.
The work boat I ran has 2 gens. I supervised the installation and managed the maintenance. Both have been run at moderate loads and properly maintained. As of 3 yrs ago when I stepped off the boat Gen #1 had 22,000 + hrs, Gen #2 had 18,000 + hrs. Both are Isuzu 4BD1. They have required in addition to maintenance some minor repairs. Water pump, thermostat, injectors. Both are still running strong.
The main is a Cat D379. When we acquired the boat the hour meter was broken showing about 8,000 hrs. We have no idea the real hours but it was in bad shape requiring an in frame overhaul. The hour meter 3 yrs ago showed 27,000 + hrs. Due likely to poor care by the previous owner / operator the main has required regular repairs to keep her running.