You may also want to check the list of devices that support the current cersion of iOS 13 so you can still able to develop the app for at least 2 to 3 years to come.
iOS 13 ended support for all iPhones using the
Apple A8 SoC or earlier and having less than 2
GB of
RAM. This also marks the first time support for
32-bit devices was dropped completely (e.g. iOS 13 is compatible on devices with a
64-bit architecture only). Devices not upgradeable to iOS 13 include the
iPhone 5S,
iPhone 6 / 6 Plus, and the
sixth-generation iPod Touch.
To further
differentiate features between iPhones and iPads, Apple has
rebranded the
tablet-oriented platform with its own operating system,
iPadOS. The
iPad Mini 4 and
iPad Air 2, which use the
Apple A8 and
Apple A8X chips respectively, support
iPadOS 13 because they each have 2 GB of RAM.
Source:
https://en.wikipedia.org/wiki/IOS_13#Supported_devices