iPhone 5S started on iOS 7 released on September 20, 2013 and received a full upgrade to every version of iOS up to and including iOS 12 when it was dropped in

iPhone 5S started on iOS 7 released on September 20, 2013 and received a full upgrade to every version of iOS up to and including iOS 12 when it was dropped in iOS 13 in 2019. After that happened, Apple went back and backported security fixes to iOS 12 with the latest release in June of 2021. Thats 6 years, 5 days of "full updates" if you consider the release day of iOS 13 to be the end of life support.