Could I have a female friend that I intend to marry

As you know the age to legally marry in the US is 18, and to my parents the age at which we decide my wife is 25 or later. So basically as a teenager I can't have a wife and dating is of course not allowed, so no romance with a girl at all. But, what if I had a female friend that is also a Muslim, and what if I like her, think she has a good personality, and is my type so I intend to marry her later. She knows this and also thinks I'm good partner material and wants to marry me too and openly stated so. The relationship between us would still be platonic but of course its hard to say "I wanna marry you when I can" without stepping over the line sometimes with some flirting or affection. It isn't as much affection or flirting as a couple but it is still present. Is this relationship haram?