iOS 11 is a 64-bit only operating system. That means that any phone made before the A7 chip was released won’t be able to upgrade to iOS 11.

The first iPhone with the A7 chip was the iPhone 5s. The iPhone 5 and 5c do not have the A7. The iPad Mini 2 does have the A7. The iPad Air does. The iPad 4 (iPad with Retina Display, released September 2012) does not.

As to your apps, head over to Settings > General > About, then tap Applications. You’ll likely see a list of applications under the heading NO UPDATES AVAILABLE. Those are the apps you’ll likely lose access to if you upgrade to iOS 11.

Once you make the transition to iOS 11, if you follow the same path, you’ll see a similar list. If any of these apps are critical to your workflow, check with the developer to see if there’s an update planned. If not, start looking for a replacement and a way to port any data you may still need.