The oldest supported iOS 12 device is the iPhone 5s. In most cases, the iOS 12 experience is noticeably superior with faster app launches on top first-party and third-party apps, less dropped frames when scrolling, much shorter delays in the keyboard appearing, and more.
So if you are not planning for an upgrade, this is good news
See it for yourself
Layby Easy Finance
High Quality iPhone and iPad for sale
Affordable phones and we ship country wide