Answer:
The distance from the top of your head to the floor standing up straight.
Why is 6 afraid of 7?
A young man wants to have it, but when he has it he no longer wants it. Blade in hand he attacks it And does his best to remove it. Yet he knows that it is all in vain.
A tower at the root of all confusion.
Sometimes you feel it weigh a ton. Yet it is nothing, but somehow still there. Makes you uncomfortable around anyone, But speak its name and it's gone.
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.