A fantastic article on CruxCrush.com debating the merits of youth being allowed, or perhaps in other words 'being let' compete against adults.
Highly recommended reading.
Personally, and taking this from my own experience when running the comps in Ireland, I based my own opinions and thoughts off information and research from looking at other large sports (exactly as the article above did). I came to a similar conclusion that there must some sort of minimum age limit, and I believe this should account for mental and physiological issues, and after that it should be anyone's came (i.e. they can compete against anyone).
The physiological issues are the ones where potential joint injuries can happen as the body grows and matures, and the mental issues were the psychological challenges of competing in pressure situations.
After that, I believe that kids should be given the option to compete so long as they are given sound, rational advice from the coaches on whether it is the correct thing for their current capabilities. I also believe that as they are the future of the sport, and will most likely be competing at even higher levels in the future that they should be allow to compete in any and all categories at the same time, even if it means they could potentially win all categories. My logic is this - realistically, the youth should not be beating the top-level adults at all. Their power levels aren't fully developed to peak and thus a fully trained adult should be able to be a match for the youth on most occasions (I'm sure there'll be exceptions to this like in any competition where some people have an off-day and don't perform to their peak - but this could affect the youth just as much).
What are your thoughts?