Earlier quoted context omitted.
The iPad Air 2 was notable for being a powerhouse. The successor was actually slower. I guess iPadOS was in the oven for a long time.
Age doesn't make hardware incompatible with an OS. Architecture changes do.
So a windows xp machine "could" run windows 10 but you don't really want to. In apple's case you can't downgrade your OS version, and I've seen an iPad 2 go from "smooth and fluent" to "crashes before I can even unlock it" from OS updates.