Why did you apply for a 6th Form Scholarship if you didn't think you were mature enough to commit to the length of service, or hack university?
Beacause he was immature, why else?
Why should they believe you've changed?
Because he is demonstrating the maturity to know that he was immature.
I have sat on a few appointment boards, only civillian and I have to say that the fact that you took time to think about it would be a plus with us.