It isn't years it is mileage. Hot-cold-Hot-cold opens up the seam.
Mine is 22 years old.
Hot engine compartment (aftermarket headers) and UV (no engine cover or mesh cover, etc) will also reduce life. The first is related to my desire to ceramic coat my headers and the second (along with not wanting a rattling rear glass) is why I'll always have an engine cover (or if that changes for some reason, I'll get the NSX-R cover thing).