I'm not an expert on this, but I'm pretty sure that Sen. McCain is a "natural-born citizen" and thus eligible to be President: He was a citizen from birth, having been born to citizen parents (his father was stationed in the Canal Zone). My sense is that "natural-born citizen" is most plausibly interpreted as being a citizen from birth.Your "100% certain" is Mr. Volokh's "pretty certain" and "most plausibly interpreted".
Read the other article cited, there are several. It nails definitively and conclusively both the common-law and statutory understanding of natural born citizen. McCain is in.