Earlier quoted context omitted.
Too short IMO, I personally would value having a 5yo device still useful, above that I can accept limitations in terms of new; below it's just pushing for renewal for no reason.
Batteries don't last that long still, last I heard you get about 1000 charges before you need to do serious maintenance to a phone, in which case you'll probably want the latest and greatest anyhow.
Why, if it still works fine?
//Nexus 7 (2012) user here