What’s the oldest iPad i can buy

this one from 2022 iPad 10.9-inch (10th generation) - Apple

is the oldest they sell from new

The currently available YouTube App requires iPadOS 15.0 or later.

For information, here is a list of the highest version of iOS supported by all models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:

32-bit devices (obsolete)

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 12.5.7

iPad Air2, iPad mini4 - iPadOS 15.8.3

iPad5, iPad Pro (9.7"/12.9" 1st generation)* - iPadOS 16.7.10

iPad6, iPad Pro (10.5"/12.9" 2nd generation) - iPadOS 17.7.2

(*) obsolete

Newer models are all able to be updated to the current version - iPadOS 18.1.1

• iPad Pro 13" (M4)
• iPad Pro 12.9" (3rd generation and later)
• iPad Pro 11" (1st generation and later + M4)
• iPad Air (3rd generation and later + M2)
• iPad (7th generation and later)
• iPad mini (5th generation and later + A17 Pro)

Seeking the oldest model iPad that can run iPadOS 15.x (e.g., iPad5, iPad Air2, iPad mini4) is perhaps unwise. As App Developers inevitably increase the minimum OS version supported by the App or associated services (e.g., YouTube owned by Google), older devices may soon be unable to access the services that you wish to use. If you choose to purchase an older model iPad that cannot be updated, its usable life for your needs may be very short.

As such, choosing a much newer model iPad will help to ensure that you can continue to use specific Apps and online services for longer. If your budget will allow, you would ultimately be best advised to consider the cheapest iPad that your can afford that supports iPadOS 18.x.