Icecone, in regard to your English, it's passable based on what you type. Trust me, I read some quotes from the CX Bulletin from people that made it into the cadet pilot program and one of them said, and I quote "I plan to improve my English."
So, as important as this might be, it isn't the MOST important thing. The most important thing is understanding yourself and being true to your character while at the same time having respect for the people interviewing you and having respect for the company you are applying for.
In regards to attitude, being childish will sadly not help. Having "dreams" will also not help. They want cold, hard proof with little gravy that you are up to their standards, that you want this and you have to be able to prove it to them, despite your age.
In the end, the only remedy to character is living life and growing up a little. There's nothing to lose I assume by finishing University, gaining experience in the corporate world (which is another big big plus for them) and then trying again a few years down the line.