I am curious about something : how does salt water use affect a boat versus a fresh water boat ? Will a 20 year old salt water boat be much "older" than a 20 year old fresh water ? What would be affected the most on the boat ?
Salt is much more corrosive. Generally speaking salt water will beat up a boat a lot faster than fresh water. A well maintained salt water boat will probably be in better shape than a poorly maintained fresh water boat.
But all other things being equal, especially involving metal and engines, salt water beats things up more than fresh.