He did seem to be aging in stages, just like the planet. It's too bad that one of the stages coincided with his pon farr...
The novels maintain a continuity of sorts on Saavik's backstory, making her the adoptive rather than biological "daughter" of Spock. Whether Vulcans would feel shame for banging adopted family members is completely unknown; it's hardly a constant for humans, either.
Very true. One also has to consider, and I think this was already pointed out, that in Amok Time Spock had hoped to avoid the Pon Farr all together due to his human side. It did delay it till he was in his 30's. The whole scene is creepy and kills the momentum of the story, like the dark cave in Empire Strikes Back, but instead of fighting himself, a student has sex with a mentor who is himself a teenage boy. Its so bad that Saavik is never seen again in movies short of a tiny bit in STIV. Its like hey Saavik want a ride back to earth, oooohhh noooo I will take the next BoP, good luck at your court marshal. I could be their as a character witness regarding your brave actions on Genesis planet but, nooooo