Re: how old is too old?
My fiberglass boat had her 50th birthday this year. No structural problems, no leaks. Of course over the years she has had new rigging, new sails, new windows, new wiring, a major interior refit, repaint more than once and a new engine. But the hull and deck came up 'good as new and better than many much newer production boats' according to the last survey three years ago.
I will be at room temperature long before this boat is past use-by date.