Other than depreciation, it's not about age. In this respect one cannot compare a boat to a car.
It's about how well the previous owner has maintained the boat and replaced things when they needed to be replaced. Another bonus is when the previous owner has added the right kind of equipment
because typically, this equipment
depreciates down pretty quickly. So it becomes his expense and not yours.
Buy a boat older than 7 years old that has had some time to depreciate down. Consider only those boats that have been kept in bristol condition. Fixing up a bunch of stuff that needs to be replaced or repaired can add up to far more than you anticipated.