The Catholic schoolgirl thing is certainly difficult to justify. So many ifs and buts. "Grade school" is not really a term used in Oz (at least not in my era), so I may be way off here, but those uniforms are worn right to the senior year of highschool, so, the guy *could* be thinking of 18 year old (at a stretch). But in an adult cam site scenario I think it's best for both models and users to err on the side of caution and not reference it at all.
The "Daddy" thing, is another issue. Theer are a few possibilities, in one instance,
@BlackWizard is correct, it stems form sugar daddy. Marilyn Monroe in
Gentlemen Prefer Blondes refers to her beau as "daddy" he is not that much older than her, but is extremely wealthy, so it is not a father figure thing at all in that instance.
As to models using it, if they are Colombian it may merely be a translation issue. Both Mami (mummy/mommy) and Papi (daddy) are/can be terms of endearment for one's partner. I have even seen/heard in some Colombian TV shows parents calling their kids mami or papi, it clearly can mean sweetie or sweetheart or whatever directed at anyone of any age. So if an inexperienced model were to translate papi to English for a conversation it would come out as Daddy and may not be corrected.
Then there is the Fleetwood Mac song
Oh Daddy, I do not think Christine McVie is singing about her father, nor about a father figure partner. I am not sure exactly what the motivation there is.
But again, if I was a model (and as a user) I would not use the term, and would discourage it's use by anyone interacting with me on a cam site.