The line is actually "you ain't as green as you are young," meaning he knows that though she is young he knows that she has slept around and is sexually experienced. For instance, if she was beating around the bush and trying to play hard to get then he's cutting right to chase saying basically, "Come on, Sweetheart. Don't play dumb with me. I know who you are and you know who I am. Are we gonna stand here all night or what?"
The line is actually "you ain't as green as you are young," meaning he knows that though she is young he knows that she has slept around and is sexually experienced. For instance, if she was beating around the bush and trying to play hard to get then he's cutting right to chase saying basically, "Come on, Sweetheart. Don't play dumb with me. I know who you are and you know who I am. Are we gonna stand here all night or what?"