I can't see anything at all wrong with mentioning a birthday at a restaurant. It is pretty much standard practice at lots of restaurants (not just at WDW) to do something to celebrate a birthday - a cupcake, a silly song, whatever. Obviously, they expect people to let them know when they are celebrating a birthday - no matter what age the person is. When I took my sister to Cindy's for lunch on her 22nd birthday, they decorated our table with confetti, gave her a dessert with a candle in it, sang to her, and gave her a nice certificate. When I celebrated my 29th birthday last year at the San Angel Inn they gave me a little cake and a card signed by Mickey and the waiters. Obviously they wouldn't have had all that cool stuff back there if they didn't expect to be celebrating lots of birthdays. Pretty much every sit-down restaurant I've been to (Chille's, Abblebee's, Olive Garden, Red Lobster) does something for a birthday. Would I expect a free meal or a huge cake or flowers or anything elaborate? No. Would I share that is was a birthday, anniversary, etc. in hopes of getting a free room upgrade, flowers, a champagne basket, etc. No. But I think a free cupcake and a Happy Birthday song is different. I wouldn't be upset if nothing at all happened, but since it is so common for restaurants to do something, I wouldn't see any harm in mentioning it. I think the restaurants expect and want people to mention it.