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

https://knoxuqsk688.cavandoragh.org/what-should-a-roof-survey-focus-on-for-an-older-single-ply-membrane

Single ply roof guarantees usually cover 15-20 years, but the actual service life can be 25-40 years or more. The guarantee often focuses on materials, not wear and tear from weather or maintenance