This is regardless of his mothers age, marital status, the citizenship of his father, any other citizenships he might be eligible for, the opinions of a French legal scholar from before the United States existed, or Jerome Corsis (who is often wrong about most everything) interpretations of law.
...you are correct.
Not according to the Supreme Court. The 14th Amendment did not affect the preexisting requirement in Article II, Section 1, Clause 5. Nor does any law passed by Congress affect that requirement. There would have to be a constitutional amendment to affect that requirement.