Hi Angel.
No, you don't need to be 18. However, if the manuscript would be accepted, then there are contracts to deal with, in which case, your parents would have to sign the contracts. Before writers submit to publishers, though, they usually go through an agent. The same idea comes into play with an agent--plenty of them say they will take underage clients, others prefer not to just because of the extra step when it comes to dealing with contracts. I believe the number of agents who prefer not to represent underage contracts is far fewer than those who are willing. It's just a matter of a good book.
We have a handful of writers here on AW who got agents and were published before 18.