Goes up, never come down

My little cousin sister: I ask you, what goes up and never come down?
Me: (without thinking) Petrol price!!! (it hit a high USD100 per barrel few weeks ago. I observed an increased in petrol price ever since I got my license!!!)
Cousin sis: (without giving me a chance to explain myself) No! What goes up and never come down?
Me: (scratching my head and think really hard) Price for necessities? You know recently flour increase already, make our daily meal so expensive ... ... bla bla bla
Cousin sis: (impatiently) No! No! Faster! What goes up never goes down???
Me: erm .... erm ... erm ... (i am thinking of share, but where-on-earth can share price goes up and never come down? I must be kidding myself) I don't know the answer. Sob. I surrender!
Cousin sis: aiyo, your age lor! Your age keeps going up and will never goes down.
Me: ohhh, you are right, why didn't I think of it. You kids are really smart nowadays ar!

These two kids are having great fun singing, with action as well =D