Answer this riddle BQ inside?

[Amazing Kid]

I am constantly moving
I cannot be regained once lost.

10 points for the first person who gets it

 

[leon]

a girl

they move on from guy to guy

and if u didnt get to hit that and u lost her u cant ever hit it again :O

 

[onemantandem]

Your heart

 

[Anneliese]

Time? age? air?