Is it wrong to be a 43m and dating an 18-year old because her body is phenomenal
That's a big age difference. Is her body more attractive to you than someone closer to your age?
It is but her attitude is not good. She doesn't keep up with me and she thinks she knows too much about me.
It's great you found a girlfriend, but she is too young for you and you are too lustful. You only take pride in how she looks, and not her personality. You are very shallow and your relationship won't last very long.
I don't care, I'm thinking of marrying her anyway.
I'm sorry, but I really think you're too old for an 18 year old. Marrying her will only cause you and her problems, especially since you only like her for her body. You would be better off to find someone closer to your age and more compatible with your personality.