Single ply roof guarantees often cover 15-20 years, but the roof can last 25-40...

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

Single ply roof guarantees often cover 15-20 years, but the roof can last 25-40 years with the right care. Guarantees typically focus on materials, not wear and tear or maintenance