CNYC, the question wasn't "Who is a citizen?" the question was "Who is a natural born citizen?" Obviously, if the mother wasn't old enough to qualify him as a citizen at all, the "natural born" part doesn't matter. But the definition of "natural born" disappeared sometime around 1795, and it has been a subtle, mostly unaddressed question ever since.
The question may (or may not) also apply to John McCain (born in the Panama Canal Zone), Lowell Weicker (born in Paris, past tense, I doubt he'll run again), and Mitt Romney (born in Mexico).