Next year my mid 2013 MacBook Pro will be 5 years old and the thing still smokes most lesser PC laptops. The battery still has more than 50% of the charging cycles left and it all runs really well. I figure I’d keep it until it died which could be another 5 years.
But in any case Macs and iDevices are different; Macs tend to stay backwards-compatible for quite a while longer. 32-bit apps still work fine and will as long as Macs are on Intel processors. Even Carbon[1] apps still work (compiled as x86 binaries) on the latest MacOS, and those will also run (compiled as PPC binaries) on MacOS 8.1, from 1998.
[1] https://en.wikipedia.org/wiki/Carbon_(API)