Susan,
I'm only 23 myself (and have no idea regarding my own maturity
) but i know that if my mother said anything negative regarding one of my boyfriends then i would definately be hurt and offended. My current partner has a brother that sounds quite similar to your daughters boyfriend. Basically his behaviour is a direct result of never having to take responsibility for his own actions. Perhaps you could sit down with the boyfriend and explain that if he wishes to remain living with you, then he will have to pay board and live by your rules. This means that he may have to get a job (if he doesn't have one) and this will minimise your contact with him and possibly force him to grow up a little. I don't think that you should tell your daughter how you feel unless you are absolutely positive she won't take it the wrong way, and as you describe her as immature then this seems unlikely. If your daughter gets mad about you asking him to pay rent explain to her that you can't afford to keep paying for him but you really want her to be happy and that this is the only way that you can keep him close. This has the added bonus of possibly making him move out/get a job etc while making your daughter think that you are the good guy.