I think the perfect place is the 50's Prime Time at DHS. First, 50 is in the name and second, he was born in the era that the restaurant is decorated in, and the TV shows that are on the screen.
For your birthday, they will usually do a whole birthday song, cupcake and crowd participation. Usually, they will bring a birthday card and your server will get everyone in your section to sign it. A lot of people really got into the act with mine.
If you're not aware, the restaurant is themed like you're at Mom and Dad's place, and your server is usually a "cousin". Some of the folks who signed my card used the "cousin" name, too! The cutest thing was later in the day, when I was waiting for the family to come out of the Great Movie Ride and someone yelled "Happy Birthday Sharon" from far away. I thought who could that be, so I waved and he said "It's Cousin John and Sally from lunch!" So cute!
Anyway, I thought the theme was perfect for a 50th. Let the server know it's his 50th, and get into the spirit of things the whole dinner. Make him set the table, make sure he has a birthday pin, call your server cousin, eat your veggies, etc. Once they know you're really into it, they will hopefully make his birthday over the top (as long as that's what you want).