My iPad manufacture date
Date of manufacture
iPad, iPadOS 14
The approximate date of manufacture might be determined from one of the serial number decoders that you might find on-line. You’ll have to search for these resources yourself.
If you are instead attempting to establish the release dates for the various iPad models, you can find also find this information online. A good (unofficial) source is Wikipedia. Another source of model data is the Mactracker App that you can download (for free) from the App Store: