I'm going to chime in here in agreement with BigGuy. Your boyfriend is choosing to remain 'under the wing' of his parents, and they are treating him as child because of it. Until he moves out and becomes independent from them I feel like they do have a right to some say about his lifestyle and relationships.
I don't think there is anything you can or should do to change his relationship with his parents. It's his job, as an adult, to do that.
Take Care, good luck to you and yours
"Owning your feelings is basic to understanding the boundaries of where you end and the next person begins and the perfect first step toward self-acceptance and self-love." The Ethical Slut pg 69, Dossie Easton and Janet W Hardy
Scarlet's Blog: http://scarletsredletters.blogspot.com/