Yeah, seems like a support group might be a good bet.
Also, if you're that close to 18, I don't see how fudging an online profile just a twinge could be that serious. I don't know the exact age of consent laws of Australia, but assuming you met someone in their early twenties or younger, I highly doubt anyone would be breaking any laws. Look it up to be sure. You should let someone know your real age probably even before your first meeting though just to get things off onto the right foot.