How do I deal with an immature brother?

My brother is 25, but acts like a 13 year old with no manners. The guy talks about crude things like toilet talk all the time (farting, etc), and is a slob. He will wear a stained t-shirt for days instead of cleaning it. He never dated, because he thinks saying stuff like hey baby wanna go back to my place and do it to girls he never met is a pickup line. When I was younger and started dating, I did my best to try and avoid bringing her around him and could play his lack manners off as being a kid who hasn't grown up yet. The thing is now that he's 25 and I'm getting more serious into dating, and they wanna meet my family they are gonna wanna meet my family and eventually gonna have to meet him. I don't want her to be so turned off by him that she runs the other way, its embarring. I have tried to talk to him before, and he doesn't listen. What do you think?