Single ply roof guarantees usually run 15-20 years, but the actual service life...

https://claytoncllo171.tearosediner.net/why-do-roof-problems-show-up-after-two-winters

Single ply roof guarantees usually run 15-20 years, but the actual service life can stretch to 25-40 years if the roof’s looked after properly. The guarantee covers manufacturing flaws, not wear and tear or poor upkeep