Single ply roof guarantees of 15-20 years cover material and workmanship, but...

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

Single ply roof guarantees of 15-20 years cover material and workmanship, but the actual service life can be 25-40 years with proper care. Factors like weather, maintenance, and installation quality all play a role