Completely agree re size / puberty etc. We arranged a few inter-club games based on size rather than age - the best technical players naturally rose to the top (and the experience of the comparatively older players showed, in fairness), but it was a good lesson in showing boys/parents the truer order of things. Same applied in cricket too. I know NZ junior rugby is size rather than age-based, and from u12 onwards, that would make huge sense here too.