11 years old really?

Skywalker and Zaber spent the night at my dad's house on Friday night. My dad doesn't have much patience so I don't think he'll be taking them again for awhile. He said Skywalker was fine until dad's girlfriend's son who is 14 or 15 got up. Then Skywalker was talking about inappropriate things. For example dad's g/f said she was going to take a shower and Skywalker got a grin and said "oh, can I join you?" and G/F said "I don't think so". WTF?!?! Really? What is going on? Dad called me this AM to tell me about it and said that he's said comments like that before in the past. So I am going to have to have a talk with him. I know he's going through this stage where he thinks it's funny to talk about boobs and stuff . I'm going to have to sit him down and have a talk about how it's inappropriate. I am not looking forward to this talk. In a way I think it's that he's wanting to "fit in" and with the asperger's he doesn't know how to so he thinks he's being funny. Another thing he says is stuff like "I have a girlfriend AND a boyfriend ha ha ha" just joking around. I tell him all the time that it's not funny but he doesn't seem to get it. Now that I hear what he is saying around my dad I wonder what he says around other people when I'm not there. Ugh.