Fiberglass boats have a life between 25 and 40 years depending on how well they've been cared for and how many waves they've pounded through. Wooden boats can last longer but usually don't because they require more mantience and once they start sliping they are more expensive to catch up with.
All boats start to get harder and more expensive to keep up as they age. Everything from the mounting bolts for the rudder, to the sheaves in the mast head have a life span. As all the parts start failing it gets expensive to keep replacing them.
If the boat is currently 40 years old, you need to be asking how much time and money do you want to be spending refitting and repairing your boat, as compared to sailing.
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