First, there is Matthew Broderick who was 21 at the time but looked convincing as a teenager. He played enough roles as a teen or young adult that it is difficult to think of him as being in his late 40s.
This was the first movie to feature hackers or home computers (the IBM PC hadn't been introduced when the movie was made). The computer that Broderick uses is an Imsai 8080. It was one of the first home computers made (I think it was the second). By the time the movie came out, the computer was obsolete. Most home computers made by 1983 were plain boxes, much like today. The script specified this computer, probably because it had lots of switches and lights.
When the Imsai 8080 came out, computers didn't have a bios to tell them how to load the operating system. The very first home computers didn't even have an operating system. In order to run a program you wrote it in assembly code on paper then hand-translated the assembly code into machine instructions. Finally, you used all of the switches on the front to enter your program, one bit at a time. This required toggling at least 8 switches per instruction.
The movie was meant as a message movie about nuclear disarmament. It begins with a sequence where a couple of soldiers log into a missile silo. They are given the order to launch (as a test) and fail. As a result the human element is wired out of the launch sequence. This sets the tone of the movie and is a plot point later when a self-aware computer decides to initiate a nuclear strike. The first time I saw the movie we got in late and missed the opening sequence. This changed the tone of the movie completely. I was quite surprised how different the tone was when I saw the whole movie.
The movie features a self-aware computer, the WOPR. From it's case it seems to have been built in the 1950s but it is still far advanced over 2000s technology. That's movies.
Here is a link describing how the technology was set up.
In 1983 the nation was convinced that we had to do something immediately about nuclear disarmament before the world ended. Compare that with today's urgency about global warming.