The iPad Air2 is capable of update to iPadOS 15.7.8. The Air2 does not support iPadOS 16.x. as the internal hardware does not meet the minimum technical requirements (CPU capabilities and available RAM) for newer versions of iOS/iPadOS.
For information, here is a list of the highest version of iOS supported by the older models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:
32-bit devices
iPad1 - iOS 5.1.1
iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)
iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)
64-bit devices
iPad Air1, iPad mini2 and iPad mini3 - iOS 12.5.6
iPad Air2, iPad mini4 - iPadOS 15.7.8
Newer models are all able to be updated to the current version, iPadOS 16.6
- iPad Pro (all models)
- iPad Air (3rd generation and later)
- iPad (5th generation and later)
- iPad mini (5th generation and later)