How to import photos from new iPad 5 Mini to old 2015 MacBook Air, OSX 10.9.5
Apple say that this iPad requires OS X 10.11.6 or later and iTunes 12.8 or later to sync with a Mac, so I'm going to guess that you're out of luck trying to use it with iPhoto.

You could try:


Seeing if you can download the photos using the Image Capture app on the Mac (Launchpad > Other, or find it in the Applications folder)
Transferring the photos via a service such as Dropbox
Upgrading the Mac to a more recent version of macOS - it should be easily capable of running the latest version and give you a better experience all round. 10.9.5 is pretty old now and is no longer supported with security updates etc, so it's a good idea to upgrade. If you really don't want to go straight to 10.14 for some reason, this Apple Support page has links under Learn More from which you can get the previous three versions.