I have 20-something machines, I've sort of lost count. 22 or 23, I think. Almost certainly not more than 25.
Four are modern machines that I've bought brand-new over the years, starting with the simple Kenmore I bought when I was 19. One of those 4 is an embroidery-only machine.
A couple more are machines I inherited from my grandmother (including an industrial Pfaff that is an awesome and slightly terrifying BEAST, I love that thing).
The rest are mostly machines from the 50's & 60's, that I bought mostly because I think they're awesome. I do have a few that are older, including a hand-crank Singer 28 from 1899 and a few are from the 20's-40's. The oldest machine that I use on a really regular basis is my Featherweight, it's from the 40's. I have mostly Singer but I like a lot of the Japanese zig-zag machines so I have a few of those too.
I keep 4 or 5 machines set up for use at all times, and tend to rotate the older ones through so they all get some love. I try not to let them sit for very long without getting put to work. I have four "students" - friends who are beginner sewers that come over to work on sewing projects and I try to help them along - having several extra machines set up makes it so they don't need to bring their own machines if they don't want to and helps me keep my various machines limber. Plus I like introducing young people to vintage machines! (2 of them are in their early 20's.)
Kind of funny, some of you might relate - the first time my house sitter came over, she surveyed my sewing room (which is in the living room) and looked at all the machines set up and asked me, "So, how many people work here?" She seriously thought I was running a sweat shop out of my living room! LOL!