Yeah, hopefully someone will post the citation. I can find this referenced on this site and by googling, but no one ever mentions the source of the law - frustrating. I am also not finding it on find law - but that is keyword driven, so not so surprising.
Basically - though - If I understand you - no one whose parents were under the age of 19 at the time of conception could become citizens. Is that correct?
Firstly, the law didn't state "conception", but birth. Secondly, I may have left out an important detail (recollection and all), that this law only applied to children born in a foreign country to one US parent.
As I said earlier, the exact statute was posted here on FR many, many times back in November, when the issue was burning up JimRob's bandwidth. It's here.