[DiogenesLamp]

“a person born outside the geographical limits of the United States and its outlying possessions of parents one of whom is an alien, and the other a citizen of the United States who, prior to the birth of such person, was physically present in the United States or its outlying possessions for a period or periods totaling not less than five years, at least two of which were after attaining the age of fourteen years”—8 U.S.C. § 1401

That might be the current law, but I believe the law at the time Obama was born is more stringent regarding the necessary residency in the US prior to birth of the Child. If I recall properly, it required five years of residency after attaining the age of 14.

Of course this begs for the question, why doesn't a "natural citizen" have a mother residency requirement?

A natural citizen has neither a residency requirement for the mother, or a residency requirement for the child. A natural citizen has to meet no further requirements to keep their citizenship.

[Nero Germanicus]

Yes that’s correct. Stanley Ann Dunham would not have qualified. She would have been three months too young. She was born on November 29th and her son was born on August 4th. She would have needed to be 19 and she was 18 and 9 months.
But the state of Hawaii says that he was born there, so the point is moot.