CFS played Aussie schools in year ten as a 15-year-old (09-11). The poor bloke couldn't catch a break with injuries. He's still 29, which is bloody hard to believe.
It's hard to look past the size in the juniors, especially when a bloke dominates. I guess the difficulty is ensuring they develop their skill set and aren't left behind when everyone else catches up. There was a very good chance that this could've happened to Will Skelton. Maybe we have Uni (and French rugby) to thank for that one.
As far as pure size goes, I'm unsure if the leaguies have much to offer. There's no inherent advantage in being 200cm+ or 5'11" and 120kg. It's the dynamism, power and balance that are the most attractive attributes. We should be looking for well-balanced ball players and edge backrowers (15-16yo's) who have played a bit of rugby growing up.