Is It Normal For Me To Have An Imaginary Friend?

I'm a teenager, and I have an imaginary friend. His name is Arthur, and he's very handsome, and very empathetic. He has black hair, which he slicks back, dark brown eyes, sometimes he has stubble on his face, and he gets dimples when he smiles. He's sort of based of guys from the Roaring Twenties, and he's also based off of the character Arthur, from Inception. He dresses really well, like with dress shirts, dress pants, and vests. I often talk to him for advice or opinions, or just to talk. He's into a lot of the same stuff I'm into, and he's a good friend, but he's also kind of like a mentor, and sometimes even somewhat of a boyfriend(now, I've never been into older guys or anything like that, I just don't have very many options at my school. I would never go out with a guy in real life if he wasn't age-aproppriate). I have real human friends, I'm not a loner or anything. I am a bit of an introvert, and a bit whimsical. The thing is that I'm into things that not many people are into, like poetry, old movies, dreams, and all that sort of stuff. I'm a bit more philosophical and eccentric than most people. I was home-schooled until the fifth grade.  I'm a writer, so I tend to have sort of imaginary friends, like with my characters. But is this normal? I have ADHD, but I'm afraid this might be abnormal. I've read that imaginary friends are good for the brain developement of younger kids, but what about older kids?