I have an 18x18 room in my house that's been taken over by shoes. And then I have a storage locker that's temp controlled too. I've found most midsoles are fine for 10+ years. Around that 10-14 year mark the glue starts giving way so I've had to have several re-glues done, then 15+ years the actual midsole starts getting suspect. Only soles ove had actually crumble are am1 Patriots, am1 99 og reds, and og am90 Bacon. My Greystone, Shima Blue, og Curry, and others from that era are still going strong.
To be clear though, almost all of this ds stuff is from 2016 to today. I've said it before in here but I was out of sneakers for a long time. I had 2 pair of sneakers and wore flip flops 99% of the time until I fell back into sneakers in 2016. It was good timing bc 2017-2019 was an amazing time for am1.