My mom is still happily using her original iPad mini with iOS 9. Some apps these days are not compatible with it but asurprising number are still targeting iOS 9. Lots of popular apps such as Telegram, Netflix, Overdrive books support iOS 9 and still get updates (unsure for how much longer). Others like the Target app, require later iOS versions and force her to use an older version, which tend to still be functional, though without the latest features.