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

https://wiki-legion.win/index.php/Is_a_20-Year_Guarantee_Normal_for_Single_Ply_Roofing%3F

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