I have 4 out of 5 upgraded, the 5th will be soon, since the hard drive just dies (nothing to do with Windows 10) and my stuff is far from the latest.
My 8.1 machine is like 3 months old, but I just upgraded 2 netbooks that are 3 years old, a 4 year old, $250 eMachines, and an 11 year old...