I don't see how 3 years is overkill. More than likely, he will only serve a fraction of the imposed sentence. He is lucky he didn't get more time.
Society paying for sending a 17-year-old to jail.
He will lose years he could have gone to school.
Most likely keep being a burden for society.
This is the failure of the American system is not to promote moving forward but to punish. Hell, doesn't even follow the words of Jesus Christ if you want to go the constitutional way on this one.