List of all iPad models (iPad, Air, Mini, Pro) and their maximum updates

In five years, when we retire, my wife and I have agreed that we will purchase current models of iPads. Until then, we get used models. But knowing which models can be updated is difficult.

Is there a running list of iPad types (iPad, Air, Mini, etc.) and their most recent iOS updates? I don't want to purchase an iPad only to find that it won't install more recent iOS updates!

Scott