Time is a continuous function; I forget now all the other terms that describe such phenomena, like monotonically increasing.

Age, you would think, runs parallel; but no. 

Turn back time

On my birthday, I'm one year older
With each passing day, I shrink
My only wish: to grow wiser
And remain as young as I think

The child in my heart is still smiling
She’s skipping and laughs out loud
Her only wish: not to turn grey
And to make my mother feel proud

PS It's not my birthday today, but it's someone else's; and it'll be mine soon enough.