I semi-regularly ssh into a server that's running linux 2.2, and AIUI the home directories for that and the desktops in the building (that I do use regularly) are served off an ancient SGI mainframe. I also regularly use a server running AIX 5.3; I have no idea how old the hardware for that is (AIX 5.3 came out in 2004).
Thus, I'm reasonably sure 15+ years old is not an overstatement. Yay for universities.
That said, even my desktop is over 6 at this point.