how can i get into aviation mechanic for the marines?

You should discuss your options with your parents. You have chosen a rewarding career goal. You will need to study and practice all of the things they teach you along the way to discover the best way to embrace this career.

Private training schools are a good option. The Air Force is another option.

Private Training Schools teach what you need to know and have Job Placement opportunities.

Here is a website that says become an AV in two years. It has good information and a downloadable book to help you understand the requirements that need to be met to become an Aviation Mechanic.

http://www.aviationmaintenance.edu/blog/aircraft-mechanic/become-faa-certified-aircraft-mechanic-less-2-years/

A simple Google search like:

"Aviation Mechanic training" Will produce many sites that will help you reach your goal.