Recruiters have ways of getting "sealed" and expunged juvenile criminal records. In lean times they can wave certain restrictions, but there are a lot of people trying to get in the armed forces these days. You'd better have a good story (a true one), and an understanding recruiter. Even if you do, they may not be making allowances for that sort of thing at the moment. Talk to a recruiter about it, they won't shoot you for asking. You can do it by phone if you'd like.
I think yes, juvenile records are sealed right? If the recruiter wants you bad enough they can do all kinds of stuff to get you in. My step sister joined the navy with a juvie record for underage drinking. I don't know if that was a felony though
You can join the marines with a juvenile felony record. However, the marines can either reject or approve your application depending on the severity of your juvenile felony record. For more information, please consult your recruiting officer with the details of your juvenile felony record or check out http://usmilitary.about.com/od/marinejoin/a/criminal.-um-.htm.
Once you turn 18 those records are sealed. Can not be reopened. Yes you can join. Half the time they threaten to send ppl to the military for crimes if under 18 so why reject you now that you want to help. That would be stupid on their part!