@maniacalmanicmania I think it's become a lot longer over time.
Back in the '80s and '90s, one computer year was maybe 30 years if you were lucky.
If you bought a 486 with VGA and Windows 3.1 in 1992, by 1995 it was completely obsolete. Time to get a new Pentium with Windows 95.
And by 1998, that shiny new Pentium would be far too slow to run many of the programs you want.
Now? It's probably around eight years to one human year. If you got a laptop in 2015, you'd just about be getting to the point you'd probably want to upgrade it now.