To be fair he didn’t say that. In my opinion both of your opinions are correct. Most teenagers vote terribly, and those who serve should have the right to vote.
He didn't, but that would be the logical conclusion.
I'm not sure that the young voters are, relatively speaking, terrible voters. (Consider that they are still learning, consider that they have been exposed to a decade of indoctrination, consider that they don't have a lot of "real world experience".) This is a far cry from, e.g., voting for Romney in 2012 despite his record or the Republican party's lack of action on any of their platform-planks.