I don't see how it could be the 13 year old. If Vulcans got their first pon farr that early, they'd likely just marry their betrothed at that time since that was already done when they were seven. So you have minors having sex, which I'm sure the Vulcans would frown on at that age, but they could put a happy face on it by having the poor dears marry. Could probably work in some whoops babies while they're at it. Spock and T'Pring with adult spawn could have been interesting.