How long do you keep a mower

I seen on earlier post 10 years for a mower life? First of all I buy used if I can. I bought my push mowers in the 70's, my JD 1980, my Wheel Horse 1991, and my Ferris 1999 new and only one I ever bough new. The push mowers only get used for trim work so they don't get many hours per year, The JD mows my camp, Wheel horse for snow removal and the Ferris gets used hard by more then one family weekly+. All I care about is that they run and do there job. I do give them a paint job with a paint brush when they start to get scratched and rusty. I give my mowers yearly maintenance and they are in top mechanical repairs. How long do you keep your mower and when do you determine when to replace it?