I suspect in the scene that we witness she may be be establishing the psychic link that is something between a betrothal and a marriage. Although he was aging so fast he could have well reached the physical age of his first pon farr in minutes, and then again in a few minutes more, and so on... so hell yeah they did it, but how many times did they do it?
It was always intended that Saavik had feelings for Spock: the way she reacted to Spock's fake death in STII and later on to his real death were evidence of this but it was subsumed when they made her far less emotional in the sequels, which was a real shame.
Saavik's canon age is a bit vague too. Just because she is an inexperienced junior officer doesn't mean she has to be very young (Tuvok was a 100 year old lieutenant). Alley was 30 or 31, while Spock was only about 53, which isn't that old for a Vulcan. They were both much older by the time they married if an adult Picard was present at their wedding (which is more than can be said for Woody Allen).