I'm old, but sounds like not quite as old as some others here. HP-41, and have to admit that I like the HP-42 better. There's a great HP-42 free emulator for android.
41s were popular at GT, and lots of folks did synthetic programming and hot-rodded them with faster clocks. When I started working and needed a new calculator, though, I wanted something I could easily slide into a pocket, and the 15C gave a lot of punch for its size.