My friend did her son's 17th birthday party at Chuck E Cheese. It was just a couple of his friends and family and then he went out to the movies afterwards.
So yes, the kids like acting like little kids sometimes too. I know you're doing it at the house so it's not exactly the same. I would still do the pinata. Horse shoes and the ladder game are always good for parties. Maybe you can also do some fun parlor games similiar to what they do at showers.
Perhaps you could set up a trivia game about facts and events in his life. I do this sometimes when my daughters and their cousins get together (they only see each other once or twice a year). We set it up like Jeopardy! and I write all of the "answers" and assign them to categories and dollar amounts. Their favorite category is always "family facts."