Lucky in my opinion, I admire Australia a lot, but please, absolutely do attend one, at least once. It's an experience to be had. The fandom is great and being there with so many of the other ponies is pretty exciting. I wasn't sure what to expect, but I've seen how others felt about going to one and I feel like I was missing out and I was right. It's like a non-stop party and you get to do it around horse famous people from the show, the fandom and all the other con goers that are really sweet. It gives you a much better appreciation for the work that people put in for the fans and to the show.
I was thinking too, if you can't go to one locally, which is much easier, but if you want to go to one all the way up in the States, there's not gonna be a quick and easy way to make that travel. It's gonna take a lot of work and planning.
I would first plan essential stuff before trying anything else, like what are the regulations to travel over sees and you'll need to get a passport put together and other things are required. Like if you're traveling over seas under 18 I don't know if there are other documents you'll need. Knowing which con you want to go and figuring out how to get around locally, like by busses/taxies and what's in the area for food.
After figuring all that out I'd give yourself an entire year to save up, any shorter time might be too difficult. So if there's a con a year from now, try aiming for that one. I'm guessing from where you are, in total, you want to save $250-$300 a month for a year to get around $3000. That's should be enough for travel, lodge, food and spending money. If you can get full time work, that'd be your best bet. Since you're young you could try two jobs for just a month, or two, just short term so you don't burn yourself out, cause it's tough on your body. Be aware that some jobs do frown on moonlighting, but with two jobs, you might get 1/3 of the way to savings in just a month, or two.
So it'll be tough, but I think doable. When traveling, try to find the cheapest way you can find, which will take a little research too.