Since O’s mother was just 18 when he was born, she had not lived as an adult ( not minor) citizen for the required amount of time to confer citizenship to her offspring.
She was 17 when she became pregnant.
No, the law, now as then, requires that the US parent of a child born outside the US, where the other parent is not a US citizen, have been a resident for some period after their 14th birthday. It was 5 years then, since reduced to 2 years. His mother had not been alive 5 years after her 14th birthday when he was allegedly born. Thus she could not transfer US Citizenship at birth to him, if he was not born in the US. If however she hadn't been married to the father, then she could. The residency requirement only applies to a child born outside the US and with married parents, one of whom is not a US citizen. Even if the parents are not married and the father is the US Citizen, then by acknowleging his parentage, the child is a US Citizen at birth. But Citizen at birth, especially one born outside the US, is not the same as "Natural Born Citizen" (even the 14th amendment says that person "born or naturalized in the United States" are citizens. A person born outside the US, must thus be considered "naturalized at birth", because Congress wrote a law to give them that status, and Congress only has the power to define a uniform rule of Naturalization. Thus such a person, even though a citizen at birth, is likely not eligible to the office of President.