When is my iPad obsolete from a security position?

Your iPad6 continues to receive point-updates - that address emerging security issues and functional fixes. As to when these updates will cease, Apple does not provide advanced information; that said, you might reasonably anticipate security updates continuing at least throughout 2025. History demonstrates that Apple releases updates for significant security vulnerabilities for at least one to two years - and possibly longer - for devices that cannot be updated to the current major version of iPadOS.

Older devices, that no longer benefit from regular security updates, obviously run increasing risk of an unpatched vulnerability being successfully exploited by malware or threat Actor. While you should have no immediate cause for concern, perhaps start thinking about and budgeting for a replacement device within the next 12-18 months.

Again, to be absolutely clear, contributors here cannot provide a definitive answer as to when Apple will cease providing security updates for iPadOS 17.x devices that are incapable of update to iPadOS 18.x.

You're very welcome. A new iPad will no doubt be something to look forward to. 🙂