3-5 years. Why:
I could never buy my last boat first. The boating mission changed.
Many only have the two happiest days whether it is a thing just tried or a lifetime passion. Others go through phases of water missions that Require different boats in order to meet the new mission. Missions can change with age, family size, location, finances, desires, experience and so on.
Avoid the wrong boat by honestly identifying your 90% use mission. Then look at boats that will meet that Mission. Simple. Then you will have the right boat.
Reasons people sell boats at all: Marriage dissolution, others don’t share the passion as hoped, did not get a pre-buy survey done and got in over their head financially, Mission changed, or wanted to change. Could not afford to buy enough boat, so settled For less. 4-foot-itis. (Want or need four more feet) Family room needs. To downsize.
Types of boating mission: Water skiing, wakeboarding, jet skiing, fishing, lake only, river only, ocean capable, sailboating, fast boating, weekend boating, extended exploring, live aboard, passage making, commercial boating, retirement pleasure boating and so on.
I have done all these and loved it all, at the time. Comfortable efficient trawler cruising for retirement is what we like now. West Coast to Alaska. Eventually the great loop.