Ah Pauline… what a character.
I’ve been refurbishing old Android devices. I have an old Gen 1 MotoG 4G which was on Android 5.1 and a Nexus 7 2012 tablet on 5.1 as well. The Nexus 7 was rendered unusable by the 5.1 upgrade… well it worked but would freeze for 30-60secs at a time. The phone worked but there were so many security holes in the software I was relecutant to rely on it.
I’m happy to say that installing LineageOS 14.1 on the phone gives me an Android 7.1.1 phone with all the updates to March 2018. The tablet has a 7.1.1 Android as well and the lock ups have gone but it’s a less up to date image. The important thing is everything works fine on the phone, 4G, wifi, Bluetooth, GPS, camera etc. and has given me the confidence to bring my main phone up to date the same way.
If you have an old Android phone that works but no longer gets updates etc. then installing LineageOS is as straightforward as following the instructions in order. I was suprised how painless it was and will bring the phone up to date. Certainly cheaper than an Iphone X upgrade. It also means you can buy an oddball Chinese phone for pennies and update it to a European version of Android without the built in PRC spying software