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

https://daisydustmaid.com/overlay-vs-full-replacement-for-a-single-ply-roof-when-does-overlay-make-sense/

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