Let there be no confusion here. The supreme court said the punishment must be the same. They in no way argued about the length a state can impose, only that the punishment must be equal.
And that does nothing to alter the fact that yesterday, the day after Kennedy said in Lawrence that that case had nothing to do with sex with minors, the Supreme Court implied a good deal more clearly that Lawrence affects the outcome of cases involving sex with minors. (Something Kennedy and the other members of the majority must have known when he was writing his Lawrence opinion.)
You seem to be arguing that statuary rape and statuary sodomy should be punished the same. The crime is not the same and why should the punishment be the same?