I have to agree with what everyone here has said so far, some are a little more pointed where others are a little more elloquent ... the message is still the same.
At 18, regardless of riding experience (unless you are a motoGP or other professional level rider already) I would be willing to bet an insurance company will not touch you, if they do it will be for some astronomical premium price and yes, I have heard of yearly premiums higher than the purchase price of the bike
or they will write you for liability ONLY (means you gotta pay for the bike outright, no loans)
Here's something to consider, speaking from my own experience with this btw.
If you get your parents to put this bike on their policy, as you as the primary driver, your rate will still suck, though maybe not as much .... keeping in mind thats *IF* they write the policy in the first place. The down side to this is you will need to carry 10x the liability coverage that you would if its just you. Reason being, if you fug up....errr when you fug up and if it involves other people (ie not you wrecking on your own) then the "victims" will sue you and your parents (as the policy holders) .... you/they will lose and everything that your parents have worked for all their lives will be gone ... unless they are incredibly rich, in which case they can just buy you the bike outright, pay the liability coverage and be done with it. Now, my folks didnt loose everything BUT my father is a lawyer and made damn sure I carried PLENTY of liability coverage just in case. Fortunately when I wrecked it only hurt me and my bike....but I also carried in well in excess of $5 Million in liability coverage
Now in addition to all of this insurance stuff, you probably cant qualify for a loan on your own for this bike. So unless you cut a *LOT* of grass or sold a lot of it
j/k thats a whole other side that will suck at the dealer.
Again from personal experience, get something like a Katana600 or similar....you'll learn faster/safer and can probably swing the finances and insurance on that