I've got a 2014 polaris ranger 900xp that has 20k miles on it. Original engine and transmission. Replaced the clutch with a Duraclutch. I would say once you get to 10k miles that is high miles. That is also when you need to start replacing stuff. Stock polaris shocks and bushings suck. You'll be changing those every 4k miles if you use it even lightly. Go after market for parts as much as you can as you'll find alot of it is better quality and lasts longer. I bought aftermarket bushings and wheel bearings from Allballsracing.com. So far the bushings have lasted twice as long as the OEM ones. The wheel bearings weren't much better but I did buy a tool to grease those sealed bearings and now they seem to last way longer. I went with Elka shocks after my 3rd set of OEm ones. The Elkas I had set a little firmer to carry a load better and I sure like them.
Mine gets used almost daily for ranch work. It gets used, not abused. I also use it ice fishing and snaring with tracks, cab, and heater. Mine gets idled quite a bit while snaring when its below zero and also idled a lot if someone watches gates for me while I feed cows. I'm sure idling isn't good for it with lower oil pressure and such, but mine has lasted a long time even so. With tracks on it takes higher rpms to get speed as they are geared down. I putz around with mine but I'd be concerned with someone that had tracks and was a speed demon as that machine would have had the engine reved up alot.
Places that sell reman polaris ranger engines say that the engine should last between 8k and 12k miles. Longer or lower depending how it was taken care of and how it was run.
Keep the air filter clean and check often. Also change oil regularly. I used the expensive polaris oil and filters on my ranger for most of its 20k miles. I recently switched to a Wix filter and Cenex atv synthetic oil mainly for the convience of being able to buy it locally.
The ranger is the only utv brand I've had. Overall its been a good machine but rather high maintance and repairs, not sure if I'd buy another polaris or not. I plan to keep the one I have and I'd probably put a reman engine in it if it goes as I doubt anyone would give me much for it with the miles it has on it. I've got an older artic cat 500 atv with 16k miles on it and I haven't had to replace near as much stuff on it as the ranger.