I tried to download an app

Hello,

There are different ways to ensure the highest iOS that your device will support is installed on your device.

This support article has instructions about updating an iPhone or iPad wirelessly --> Update your iPhone or iPad - Apple Support

You can also use Mac and PC computers to update system software:

Update iPadOS - Apple Support

Use this support article to identify your iPad model --> Identify your iPad model - Apple Support and then the list below to find out what your iPad is capable of running. Alternatively --and somewhat easier-- is to simply try updating it and see if it will update. When updating, your device will update to the highest version currently available that it will support, or it will just say it is up to date (and can't go any higher) and won't install anything. Apple indicates ( Unable to update my iPhone 6 Plus from 12… - Apple Community ) I need to point out the obvious and state that if you want to run a higher system version than your current device will run, that you need to buy a newer device.

Here's a list of iPad models and the iOS/iPadOS versions they are capable of running:

iPad Air1, iPad mini2 and iPad mini3 will only update to iOS 12.5.7

iPad Air2, iPad mini4 will only update to iPadOS 15.7.5

These models are all able to be updated to the current version, iPadOS 16.4

iPad Pro

iPad Air 3rd generation and later

iPad (5th generation and later)

iPad mini (5th generation and later)