Start with something simple and quick, My first game took me 3 months to make, it was a big game compared to my beginner skills, when I finished the game I had learned alot and noticed that there are alot of events that I could've done in much more efficient ways, it was too heavy to be playable, so it took me another month remaking the game in a more efficient way until I was able to release it without draining batteries or killing RAM.
This way alos your big Idea game will turn out better when you have better skills.