Before you write off an old phone, check three things
Two phones, one bench. One from 2013, one from 2015.
The older one is running a system build from this March. The younger one took a modern install and couldn't live there; it's back on an eight-year-old version, where it behaves. Both flashed clean. Only one stayed.
Same bench, three things that actually decide an old phone's fate:
Memory. Modern apps and modern systems don't fit in 2GB. No build is clean enough to fix arithmetic. This is the wall that most “it's so slow” complaints are standing in front of.
Heat. A hot chip in a small body throttles exactly when you finally ask it for something. More RAM won't fix a hand warmer.
The maintainer. A phone stays alive while at least one person still builds for its codename. When the last one stops, the phone dies with good silicon inside. Check this before the calendar: a 2013 model with an active maintainer outruns a 2017 one without.
The order people usually check: the calendar. The order that matters: memory, then maintainer, then heat, then calendar.
This is a pattern off one bench, not a lab. If you're stuck on a device right now, tell me what it's doing. First read is free.
Andrew, from the bench. paper.wf/andrew-61