Single ply roof guarantees usually cover 15-20 years, but the actual roof can...

https://hectoruwog494.image-perth.org/why-do-some-single-ply-roofs-fail-in-the-first-10-years

Single ply roof guarantees usually cover 15-20 years, but the actual roof can last 25-40 years with proper care. The guarantee mainly protects against material failure, not wear and tear or damage from weather