Have seen them over 20 years old, and still going strong. It depends on the materials used during the manufacturing process. If only the highest quality materials are used, it takes 25-30 years before the pool even needs cosmetic help. Fiberglass pools have only been available in the U.S. for about 40 years and, if handled intelligently, i.e. keeping pool filled unless assisted by a fiberglass pool pro, they could easily last another 40 years. However, even the finest (San Juan) will need new gelcoat after about 25-30 years. Average quality pools will need cosmetic help within 20 years, and the lowest quality need help within 5 years. But even the lower quality pools, with help, may last more than 30 years.