A single ply roof guarantee usually covers 15-20 years, but the actual roof can...

https://www.slideserve.com/gwyneyxcez/why-do-roof-problems-show-up-after-two-winters

A single ply roof guarantee usually covers 15-20 years, but the actual roof can last 25-40 years with the right care. Guarantees mainly cover materials and workmanship, not wear and tear or damage