Indie gigs are easy to deal with. Like you said, people always want to get to the front and (depending on the type of gig it is) what tends to happen is that as the concert progresses spaces become available. Usually it's people that are too pissed or just tired from the crush of others behind them moving away to the back.

You make a fair point that there won't be as many 16-18 year olds there but as long as you're respectful you'll be fine. I know some people can be very particular when it comes to giving up space. Look at it this way, if I was stood in GA and someone came barging past I'd take issue. If, on the other hand, I got a poilite tap on the shoulder that person asked if it was ok to move forward then I'd be more inclined to let them through. There's no guarantee though as lots of people have been waiting a long time for these gigs and want their spot..a Jovi gig is a big deal, especially as we don't know when we'll be seeing them again. Not like your indie bands who have to play every week to keep themselves stocked up on rizzlas

Good luck though and have a good day out