Depends: I tend to upgrade my desktop bit by bit. I did a 100% fresh buy, case and all, in 2015 so the oldest components in are from then, but I've put some newer stuff in since.
My laptop is under 1 year old. Seeing as my old one was becoming infuriatingly slow on boot up (I think because the HDD gummed up solid for 20 mins as every program under the sun decides it's going to check for updates, update, refresh, scan, and generally fuck around with data on whatever cloud service they're linked to) and I was saving so much money not having to commute, seemed a good time.