do moving coil cartridges have a finite life-span?

Eventually most rubber or polymers will harden, but i have a Van Den Hul Frog that is 12 yrs old and it still is very good with no apparent sag or issues.

I used to have Lyra Dorian. After about 6 years the cart was worn out and needed retipping. I traded it in for a Dynavector

It's my 12th year on Shelter 501(not MK2). It was already retipped twice as it's being used long hours daily.
Other than tip and suspension on the tip there's nothing else to die that quick.
I guess with proper service and retipping ontime it'll last another lifetime.

I reinstalled a JMAS MIT-1 which is ~30 years old and it sounds great. I had sent it last year to Andy Chong,who inspected it, cleaned the stylus (vdH) and reconditioned the suspension.

A 4 year rule is in general wrong. The majority of MC can easily do MUCH more years. Before I got the cartridge bug I used a Takeda Miyabi for 10 years more or less daily and it was still ok when it found a new owner. But it was running with a correct designed Arm and the right AS, Azimuth and VTF.