If a publishing company feels your book will make money and attract an audience, they will not care how old you are. Do some research online; find a company that accepts unagented queries and one that publishes novels in the genre you have written. Find out how they want it presented (usually a self addressed stamped envelope needs to be included, and some companies want you to include a cover letter explaining the plot). Also, select a few trusted friends/family members/teachers who are willing to read and critique your novel. They will be able to point out any inconsistencies, parts that might be unclear, or give you advice on what you should/shouldn't include. This will prepare your manuscript for the readers at a publishing company, since you want to present your best work. Select several companies you want and send them your manuscript. Take all advice they give you, whether or not they select your novel. Good luck!