I did something similar in Warcraft 3, but with a Bomberman game. That wasn't my first project that involved programming though.
My first project involved creating a heavily scripted map for Medal Of Honor: Allied Assault. In that game you have the map which is created in a level editor, and then you create a level script that goes along with it. I haven't played much of Quake 3, but I'm guessing this is the "Quake C" type stuff that that game had.
My vision was to create a level that was heavily scripted that had you fighting alongside squadmates that weren't cannon fodder. There was a medic in the original game, but I wrote a medic script from scratch that was more customizeable. You could tell the medic who to follow, how many health packs he had to give to others, etc. I eventually wanted to write AI for him to take cover during battles but I never figured that out.
The level that my YouTube video shows isn't the first project I did in MOHAA, but it was the culmination of everything I learned writing scripts for that game. Everything "scripted" that you see in the video is done via the level script. The squadmates following each other, the tank encounter, conversations, truck ride, etc were all done with my level script. A lot of things are broken as you can see, and I eventually gave up when I tried to implement wall climbing at the end.
The scripts involved mainly if statements and for loops. There were also several functions, which were either called with "thread function" which would execute the function in a separate thread, or "waitthread function" which would call the function and block until it returned. I asked LOADS of questions on the Medal Of Honor .Map forums, where the people there were extremely patient and helpful, and taught me a lot about programming (especially the user jv_map, or jvmap, I can't remember the spelling).
This was done in the Summer of 2003, when I was 14 too like Vexal. Then Call Of Duty was announced (by the original developers of MOHAA that went to form their own company) and they took the vision that I had for my map and made a complete game out of it