‘In either case, he wouldn’t be a natural citizen. He would be one created by an act of congress, which is “naturalization.”’
What process did he have to go through before he could vote for the first time?
I don't understand your question. I think you have a misconception about how naturalization works with underaged people.
If an alien comes to the US and becomes a citizen, his children are automatically naturalized and they don't have to pass any tests.
Same with "at birth" naturalization.