One thing that bothers me about the episode is Spock's line after they're all back on the Enterprise. The "Ah, yes, the girl" bit. Strangely dismissive and uninterested, considering she was his wife to be and almost got either him or Kirk killed. (And it's kind of jarring to hear him use the word "girl", as T'Pring was supposedly the same age as he was - they were bonded when they were 7, after all.)
I don't think it's unlikely for males to refer to females of their age as "girl". Unless both are over 40, it's rather common IMO - on Earth, or on Vulcan.
Could get your ass kicked, though. I've occasionally given a firendly "Good morning, girls" at work, only to be roundly rebuked with a cold "We're WOMEN, not girls!"
That led me to start saying "Good morning, ladies." Unfortunately I run into someone who doesn't like being called "lady" once in a while. Maybe I'll just smile and nod from now on.