I really really want to go to CaliforniaWatch
If you'd like any advice I suggest going to uni and doing a degree you'd be interested in studying for 3 years. Maybe find a uni that does an exchange year with a university in California - then you could try before you commit? You don't have to have it all figured out right now, and it's great that you want to broaden your horizons but there's plenty of time to explore during uni and its holidays. Apply to summer camps in America, see if you can spend 3 months of the summer working there. I think your best bet is to find what interests you, apply to university for that and figure out the rest as you go along
I lived in California for a bit. Parts of it are stunning, but those likely won't be the parts you'd want to live in (they tend to be remote); but the rest isn't all that amazing. The beaches for the most part I found to be average - you'd find nicer beaches in parts of Europe, like Greece or southern Italy. Los Angeles in particular is a huge let-down, and a bit of a dump in some respects. Perhaps you should try get some experience of the place first, via something like summer work or an exchange programme as piglet33 suggested. It's an awful long way to go before realising it's not for you after all!