IBM 610 workstation computer 3355

I think he said when he was an undergraduate, so it was in college, not in high school, a bit older than a teenager.

However, some lucky teens did get to play around with mainframes or tab machines. Some got part time jobs after school doing key punching or Fortran programming for college professors. Some had fathers who worked in the machine room and could get their kids into the computer room on weekends and within limits let them fool around.

Some computers had Fort Knox level security, but definitely not all, some were rather lax. I merely walked into my summer employer's computer room (I wasn't in computers then) and asked to use the phone, I was directed to the one right at the CPU console. I could've came in off the street, I think I was only 17 at the time.

I think security was proportional to the size of the data center--a big data center (ie a 360-50 or higher or 370-155 or higher) tended to be more structured and audited with more strictness about locked doors. Smaller data centers were more informal. I don't think companies were so freaky about kids accompanying their parents on weekends when the parents had some work to catch up; now it is forbidden.