You need to have the matter sealed. This may or may not affect the military's decision regarding your fitness since they may have already seen the charge. However, if you want help in working through this matter - with the juvenile court and helping to process you military application - don't hesitate to give me a call. I offer a free consultation: 408.313.5607 Best of luck.
I agree that you should have the record sealed. As far as reducing the charge, that is going to be difficult years later. However, if you get the record sealed, you may not have to disclose it when applying for a job. There are exceptions to that, for example, government jobs.