One example of a 21st birthday wish is to tell the celebrant to enjoy this day because there are no other fun birthdays to anticipate. Another example is to congratulate the person and volunteer to buy the first shot of liquor he consumes.
Another example of a 21st birthday wish is to tell the person you not only wish them a happy birthday but that you also wish them a happy hangover. A similar example is to tell him that you do not actually remember your own 21st birthday party and that he must soon figure out the reason for that. Another example is to tell the celebrant that it has been amazing to watch him laugh, learn and grow as he pursues his dreams through many years and difficulties.
One example is to wish the person happiness as he celebrates 21 years of faithful friends and loved ones and lessons that he has learned. Another is to remind the individual that attaining the age of 21 does not mean he cannot be as immature and sexy as he so desires. A last example is to wish a happy birthday to the sexiest, funniest and most amazing person you know, other than yourself.