And your friend says "Sure" but he doesn't realize that the "age of consent" varies from state to state, because it seems to him like that logically ought to be

And your friend says "Sure" but he doesn't realize that the "age of consent" varies from state to state, because it seems to him like that logically ought to be a fixed number - in fact it's never occurred to him that it might vary - in fact he doesn't distinguish between federal and state law, just lives with "the law".