There's someone in my head but it's not me

Run, rabbit run. Dig that hole, forget the sun,
And when at last the work is done
Don't sit down it's time to dig another one.

Tired of lying in the sunshine staying home to watch the rain.
You are young and life is long and there is time to kill today.
And then one day you find ten years have got behind you.
No one told you when to run, you missed the starting gun