If you are getting your license just to buy a multifamily, don't. The time and cost to get and maintain a license are not worth the savings, and even though you will have a license you will know just enough to be dangerous, especially with multifamily. I had a friend who got a license to buy a home and regretted it. Not only did he not save much money, but he was over his head. Fortunately, he has a friend that is a broker who walked him through the transaction.
If you get your license for a career in real estate that's fine, but it is very difficult to get started as an agent, you will probably make very little or even lose money your first year, and if you're also paying for college that could put you behind the eightball. Some colleges offer classes that will satisfy the 90 hours of education required for a license. ASU offers a minor in real estate, once completed you can test for the Arizona real estate license plus get college credits.
At eighteen and in college, I think it will probably be very difficult for you to qualify for a mortgage unless you have a cosigner. Ironically, it can be difficult to obtain loans for a property as an agent because lenders are leery of the self-employed with commission income, however, if you finish college, get a good W2 job, and have decent credit, lenders will line up to give you money, assuming that you are going into a field that is in demand.
I admire you wanting to start investing at a young age, I wish I would have started investing in real estate in my early twenties instead of misspending my youth on debauchery. Good luck!