Does anybody know the answer to this joke?

[♫KBH♫]

Joke:
' What goes up and and never comes down? '


I thought it was the sky but it never went up did it?

 

[leelee]

age or sometin else

 

[katieeee]

shut

no one says shut down

 

[MangaAnimeBrain]

shut


no one says "SHUT DOWN!!"

 

[liz]

Age. You can grow up but you can't grow down.