I appreciate your ambition.
What you want to do can be done, but it will take work. First, there is finding a property that is a good investment, but I am going to assume that you can do that. Second, you will need to find a seller willing to do seller financing. There are a lot of good reasons for sellers to finance the deal themselves, but if they don't already know them you will need to be able to sell the idea. This can be difficult because even though it may be to their benefit to seller finance a lot of people would rather just take their money and run. Finally, even if you find someone willing to do seller financing, you will need to find someone who is willing to finance YOU. If you don't have a lot of money or any experience, this will be a very tough sell. The seller needs to be convinced that you can handle it (essentially that you can protect their investment). It can be done, but you are going to need to be very convincing.
My advice would be to get a job while looking for your first deal. That way you can start to build up some of your cash, and hopefully gain experience that will help you convince a seller that you are worth betting on.
Alternatively, find an experienced investor to partner with. Be prepared to do most of the work finding and putting together the deal, and have the partner there to help prevent mistakes and make sellers more comfortable with the idea of financing you.