A big part of it is built in batteries that are difficult to replace. My phone has a removable battery and has is on its third one now… still works fine and does everything I want it to, after 10 years of use.

It’s honorable that you struggle through 2013 Android, but using an internet enabled device that hasn’t received security updates in at least 7 years is a horrible idea.

Upgrade to a Fairphone at least, so you can keep replacing parts while also maintaining a base level of security.

He could be using a ROM with up to date security patches, I believe since phones from that era still have active custom ROM communities.
I was considering that, seems unlikely to me, though.
Hell you can run Android 11 on a Galaxy S2.