If you consider these releases "official", maybe, at least as far as "desktop operating systems" go. It's older than Windows; Mac OS is older, but you could arg

If you consider these releases "official", maybe, at least as far as "desktop operating systems" go. It's older than Windows; Mac OS is older, but you could argue that modern-day Mac OS isn't really descended from classic Mac OS, so it doesn't count. Sibling comment points out that various still-alive Unixes are, in a sense, still the same operating system as the original Unix. I suspect various mainframe operating systems are older and still maintained, but that's a little out of my wheelhouse.