Another popular criticism that just doesn't wash...

"It took Superman way too long to discover his powers. He's 33 and still hasn't learned to fly."

That's imposing your expectations in the world and characters. You know Superman is going to be godly powerful and tank bullets and fly at super-sonic speeds, but what reason does the character in the movie have to expect that? He had absolutely no knowledge of what the peak of his potential was until he met Jor-El, and for the most part, even if he had an inkling, why would he care. He has bigger fish to fry, that is, the world wide political implications of him being a powerful alien to begin with. It goes way beyond some personal coming of age thing. He's not a fifty year old man applying for college. Saying he's slow-to-grow or childish is short sighted.