I'm trying to use up my old shoes before buying more. My most recent shoe purchase was from November of last year, and I might get through 2019 without getting anything new. I have eight pairs of trainers currently, mostly trail shoes, and they range from 400+ to 1600+ miles. The oldest is from 2012. I also have three pairs of racing shoes that I sometimes use as daily trainers with 200+ to 400+ miles, also as old as from 2012. My most recently retired trainer was a Hoka Speedgoat 2 with 1200+ miles.
I'm doing 80 mpw with about 9000 ft climb weekly. I weigh about 160 lbs and am 50 years old. Mileage is currently divided mainly between Inov-8 Trail Talon 250 (700+ miles), Salomon S-Lab Sense 3 Soft Ground (near 600 miles), adidas A16+ Ultraboost (a laceless lifestyle shoe with the Ultraboost sole - 400+ miles), New Balance Zante 1 (800+ miles), Puma Trailfox 4 (1600+ miles).
The key to getting more out of shoes is to be able to run in more minimalistic shoes. Old shoes are like minimalistic shoes in some ways. I can daily train in my adidas Takumi Sens and the Inov-8 Trail Talon 250s probably felt thinner brand new than most runners' worn out trainers.