Is it possible to update an iOS device to a version older than the current version?
To give a clear answer to the question that was asked, which is whether a device can be updated to the latest version of iOS it supports, even if that version of iOS is no longer current.

Yes, it is possible. Software Update, either on the device or via iTunes, will offer the latest version that is supported by your device.

I can't readily find an official reference for this but it is supported by numerous other answers to similar questions on this site.