I know there are 400 episodes already and probably another 400 to go, so I was wondering if there is a point in the episodes where it's possible to use the code without watching all 400 episodes?

For example could I expect to be able to code a game such as Pacman, Asteroids or Tetris after watching the first 100 episodes? Or even the first 50?

I'm not trying to cut corners and I fully intend to watch the entire series, but I'm itching to actually create something. I'm up to Episode 5 at the moment.

The series is not aiming at doing a general purpose engine, the engine is specific to the game Casey is making. Depending on what game you want to make part of the videos will be partially irrelevant. As soon as you can draw something on the screen, read input, and output sounds you can try to make your own game and refining it after watching other videos.

I would say after the first 50 days you have enough knowledge to make a simple game. The part that is important is to apply what you see in the videos and not just watch them.

If you want to know how to do something in particular (e.g. how to set up OpenGL) you can search using the episode guide.