Possibly better suited to Biology but assuming people here will be more knowledgable on this specific area of Human Biology
It's general practice for Creatine it seems to have 'No Under 18s', however what is the reasoning behind this. Apart from the obvious, that nobody wants to try it on kids for fear of repercussions along their whole lives, is there any scientific basis to believe that under 18s would have any adverse affects to it that cause bad reactions/decline in growth, etc., as from what I can see it terms of hormones it only debatably effects testosterone (increase) and oestrogen (decrease), and in a male surely that would only have positive effects on growth due to the only minor adjustments, not pushing rates outside of the norm?
In brief, is there any reasoning apart from just fear of 'we're not exactly sure and wouldn't want to risk damaging kids' that Creatine is not recommended generally for under 18s?