What a nice 21st-birthday gift. We commend you on fulfilling your son’s dream (which, if this writer’s 19-year-old son’s dream of playing live poker in a Nevada casino is any indication, your son has probably dreamed of for a while now).
The answer to your first question is: 21 is 21, both in blackjack and on IDs. If he’s carded, unless there’s some cockamamie policy we’ve never heard of, any boss or security guard will note that his 21st birthday began a minute or two earlier and he’ll be good to go forevermore.
Your second question, unfortunately, isn’t quite as cut and dried. Some casinos offer birthday perks, but they’re generally issued by the players club and sent through the mail or via email to existing good customers. Some players clubs, off and on for example, award point multiples on birthdays (Coast Casinos did this for years), but we don’t know of any casino that has a standing birthday deal for anyone who shows up at the stroke of midnight with a verifying ID.
That said, if your son is carded and the poker boss makes any kind of deal about his 21st birthday, the birthday boy might ask if any special comps are issued for guys in his position. Depending on the boss, there just might be.
But your son shouldn’t hold his breath. Poker players in general are on the lowest rung of the comp totem pole (except maybe for sports bettors), especially those who’ve been legal to play for the past two minutes.
Two restaurants that we know of do, however, have long-standing birthday deals. Todai, the Japanese buffet in the Miracle Mile Shops at Planet Hollywood, offers one free buffet on your birthday, as long as you’re joined by three paying customers (with his two parents, your son will get 50% off his meal).
And Benihana (if you join their Chef's Table club) will send you a $30 gift certificate toward your dinner for the month of your birthday; there’s a long-established Benihana at the Las Vegas Hilton.
Also, any restaurant worth its dessert menu will usually comp a piece of cake or similar sweet with a candle if you warn them in advance –- especially for a 21st birthday in Vegas.
Good luck to your son at the tables!