If you have an inkling about what IBM 360 was.
If you actually argue about what the first PC computer was.
If you know what a TRaSh-80 was.
If you enjoyed the Zork Rap video being eaten by a Grue (or you've been actually eaten by a Grue playing Zork. Few have ever seen one, their appetite for cave adventurers being tempered only by their fear of light from a guttering torch.
If you trudged 300 feet in the snow, to the intercampus bus and drove 8 miles (uphill both ways, in blinding snowstorms) to the math center to log in to the math center to use the ARPANET (and even know what that is), writing notes on your TRS-M100 slate computer.
If you mumble 'Back in the Old Days...' with diatribes about how great certain obsolete software was...
We'll have to exclude anyone working for Google as it is well known they don't have anyone over 29, and anyone who can't mumble 'mashup xml ajax java .net' in an interview.