Definitely pick a day and make it his birthday!!!
Get the Birthday badge and live it up!!! You may very well get special privileges! I wouldn't let my kids wear the badge more than one day, but one day is enough if you get lucky!
My kids have gotten actual gifts from CM's, signed birthday cards, a phone call from Goofy inside the theme park (that one was GREAT!), tons of special attention and "insider tips", and one night a CM had the entire crowd waiting for the MS Electrical Parade sing Happy Birthday while she stood in the middle of the street!!!
Patti