I'm certain William is familiar with what would be expected of him in the manner of Kingship. Not as readied as his father, but Charles has spent the better part of 50 years in practice so that's pointing out the obvious.
I find it terribly unlikley that William's experinces thus far would make him a poor sovereign should he for some unforseen reason, ascend the throne tomorrow.
The Queen was a mere "girl" (as she has herself referred to her person in this way) at the time of her asccession and as her father's death came as what could be considered somewhat of a surprise, one could argue that she too was not 'experienced'.
William is University educated, the Queen was not, William has undertaken Constitutional studies, just like his grandmother and father before him, and has undertaken various representative visits abroad, just as his grandmother was doing at the time of her fathers death.
He may not have the years of his father measured, but the Queen was no ideal match for her father in this way either.
It would be no ideal situation for a man his age, but if it happened, he would be fit to the task. Without doubt.