I thought, too, that Spock and Kirk were meant to be roughly the same age - Kirk entered the academy 4 years later than he should have, Spock at 18 --> Spock's already graduated and advanced to commander by the time they're both 25.
Why assume his "served in SF" so late? I thought he meant he was with SF for 18 years, including the academy. Presuming the normal course takes 4 years, Spock's 36 by the time of "Enterprise Incident" which would also make him roughly the same age as Kirk in Prime Universe.
I remember in "The Enterprise Incident" Spock said he served in Starfleet for 18 years. Assuming he was 21 when he was commissioned that would make him 39, and 40 if he was 22.
Why assume his "served in SF" so late? I thought he meant he was with SF for 18 years, including the academy. Presuming the normal course takes 4 years, Spock's 36 by the time of "Enterprise Incident" which would also make him roughly the same age as Kirk in Prime Universe.