currently 17 years old. How can I start buying properties at 18?

[Eric Fern]

I am American, born and raised, but I don't live in America currently. I will be buying a plane ticket on my 18th birthday to come to the US, and get a degree with the hopes of medical school, and an eventual career in anesthesiology.

Ideally I want to take on a few mortgages, and pay them off with rental income from those properties. I don't mind getting money left over each month, but I certainly don't want to have to pay them out of my own pocket. 

I'm planning on buying somewhere I can get bang for my buck. Possibly Houston, or Phoenix. I want to get mortgages, but having money for the down payments is my problem.

Is it possible for me to find a bargain? Let's say a house is worth $150,000, but I am able to purchase it for $110,000. Can I use this $40,000 dollars as equity to get the bank to loan me the money so I can start renting out the property?

Any more tips on me building my real estate portfolio right when I turn 18 would be massively appreciated. Thanks in advance for your help!!