I need a bit of advice
 

/watch?v=RwWu0sNnero (Add onto a Youtube link)

I'm 13 years old. My voice hasn't developed yet. I suck at screaming, and I want to get better. I posted this video on Youtube to get some advice on how to scream properly. I can do a 20 second scream and maximum without gasping for air. I really need advice. Thanks.

even with proper technique i'd still talk to my doctor about it. just to find out what sort of effect screaming will have on the development of your voice. they might also be able to teach you breathing exercises for better projection.

13 seems very young to focus on what you "suck" at....
Relax dude - take it easy on yourself, life will develop your voice in the best way it knows how - vocal lessons will be helpful if you can afford it, otherwise just do your own thing the best way you know how?

Nah, mate. i'm broke~

yea you shouldbt start screamung now
it could and probably will mess up your voice

go learn guitar or something lol