Hard to Say
I remember reading an article several years ago about this very thing. Specifically, how long does fiberglass last? To make a long story short,they aquired several fiberglass boats approx 35 to 40 years old, chain-sawed them to death, sent samples to a laboratory, and not surprisingly concluded.......not quite sure how long it lasts, but fiberglass has a fairly long lifespan. Think of it this way, what are the 2 worse things in our environment? Well, it glass and plastic. Fiberglass is glass cloth and plastic resin. In Europe, fiberglass is called FRP, for Fiber Reinforced Plastic or GRP for Glass Reinforced Plastic.Anyway, it all boils down to the current condition of the boat, which will directly reflect past maintenance.Generally, an older boat like your 25 O'day would not warrant a survey due to the cost. Its not all that difficult to survey a boat yourself if you are at all familiar with sailboats. If not, try to find a friend to come with you. The most obvious would to start with taking the boat for a short run to make sure the OB Motor is good. Then check the sails to see if they feel at least a little bit crisp. If the canvas is soft, the sails are shot. Then for a more thorough inspection click on the link below. It is from a yachtbrokers website and gives information on how to inspect and what to look for. For the age you are looking at, any major problems may not be economically worth fixing.If you are not experienced in boat repairs, do a lot of reading first. Its easy to throw away money or make unsafe repairs. Also if you are tempted to take on a project, you must decide on whether you want to sail your boat or just work on it.