The oldest one that I use regularly is an IBM XT; according to the date inside the case, it was made on October 1, 1984. However, I have recently acquired an IBM Displaywriter (beam spring), which I plan to restore to working order in the months ahead.
More recently, I have developed an interest in terminal boards from the 70s and early 80s, such as those made by ADDS, Burroughs, DEC, Fluke, HP, IDT, Kaypro, Link, NBI, Perkin-Elmer, Televideo, Wyse, and Xerox, among others.