I didn't write these, they are from http://wiki.illemonati.com.
_____________________

C                    Em
Aaron, you?re twenty-one
    F
Now you can drink
(F)
The night away
      G     F           Em
So go out and have some fun
G   C                     E7
Oh, Aaron, you?re growing up,
               F
Soon you?ll be lying
      Dm7
In an alleyway
         C
Throwing up
C     G         C
Happy birthday, Aaron (you son of a bitch)
C      G        C
Have a piece of cake (you son of a bitch)
B        Ebm     Bb
Blow out all the candles
    A7     Ab        G        C
And make a wish (you son of a bitch)
B-5
(Twenty-one, twenty-one, twenty-one, twenty-one?)
His name is Aaron Ackerson,
he?s turning twenty-one.
His spiral into oldness
Has officially begun.
                D
Austin gave him nothing,
E                     F#
Grievre gave him less,
Bm                   D
Limekle gave him the finger, and
E
I gave him a dress.
C 
Spacecat, another year?s gone by
   F
It seems like it?s only been the blink of an eye
C
You?ve been rappin? and chillin? for twenty-one years
        F
Now you got no choice but to drink a lot of beers
C
?till it?s coming out your ears, so get down to Sears,
       F
Grab a mug, fill it up, raise it up and say ?Cheers?
C
You?re the flyest, tightest amateur DJ
    F
You even did a show in your Scooby Doo PJs
Damn!
D C G
Dm7              G
Congratulations, Aaron
Dm7                          G
You?re twenty-one and you?re glarin?
C                Am          G    C
You?re two years out of your teens
              F              G    Eb
And baby, you know what that means
Cm           Ab            Eb        Bb
Now you?re a man! (Man!) A man, man, man!
Cm           Ab            Eb          Bb
Now you?re a man! (Man!) A manny manny man,
Cm          Ab          Eb            Bb
A man, man, man! (Man!) You are now a man,
         Ab                   Cm7
You?re a maaaan? now you?re a maaaayon.