Tyres and motor oil both have a shelf life.
Motor oil often has a stated shelf life of about five years.
Tyres become brittle in time, the rubber becoming harder. The flexing of rubber, namely using the tyres, slows that process down. If they are used occaisionally the rubber may last about twice as long as if not.
I went ahead and placed an order for the eBay clutch kit and a set of axle nuts. Clutch could go out tomorrow or could last another 100k miles. Should it go out though, I won't have to worry about paying a million dollars to overnight the parts.