Gah! I just wrote a freaking long post about how to start and moth** f****** explorer freaked out on me but I lost it all...
So lemme resume this in a few lines:
Whatever you do, if you truly want to make games, write it all down on paper. Yeah, that's right, just make it on paper before anything else. Plan everything you wanna do with this game before you even start coding. Use tutorials and the ressources you find on the net. There's alot of them out there so just search around and you will find something that fits your needs.
Most important of all, write everything down on paper. Yeah I know, it's the second time I write this and there's a good reason for it: planning makes good games. Alot of people run head first in the concrete wall that is game development and expect to go through on the first shot. They usualy get hurt and then walk away for good. If you really want to make games, write everything you know about your idea on paper. Enemies, player moves, goals, items, levels, anything you think will be part of the game. You won't be able to list everything at first but it'll make your ideas alot more organized and clearer. Besides, games evolve as you create them so it's impossible to make one list at first and then not rework it during development.
Make your first level on paper too. make sketches of it and write down what's going to happen using a simplified sentence structure like so:
If player enters factory then
Play Alarm sound
Make light flashe red
Spawn 10 enemies of type guards
Send message to player: "Alarm triggered"
If player Shoots
Move bullet
If bullet collide with any enemy
Enemy hit energy = enemy hit energy - bullet damage
If enemy enegry= 0 or less then
burst enemy in guts
Player xp = player xp +100
Play player dance animation
and so forth. Why? Cuz it'll get your coding logic started.
Make sketches of everything in the game. Not fully elaborated pictures, just sketches that get the idea right. From the hero to the enemies, items and menus, draw everything quickly. First, it'll help you learn to draw anything and second it'll help you get your ideas straight and clean on paper.
Try to compose music too, using only your primary idea. It's hard but you'll see if you really like that. I can't really help you on that topic tho because music is definitively my weakest subject.
Starting with this "write everything down" idea will help you identify your strenghts and weaknesses. At your age, it will be important to know that because you'll have to make career choices soon. Knowing what you like/dislike and why you do will really help you.
Prepare yourself for a long and hard journey. Making games is relatively simple but good games are pretty hard to create. Read books about game design, coding, art and inspire yourself from every field of interest you have. Practise a lot too
Those are my two cents
Best of luck!