What is Average life expectancy LP 22,000 Watt home standby generator as plan buy one?

I have a stand by generator . Never been used in 6 years except for testing twice year and service.
. No power failures in that time .
So the way I see it could last a long time .
Depends on Quality of generator and how often it gets used.
is it on Natural gas ,Propane or regular gas and how well it is serviced …