With his Society assessor, I watched a 17 year old Hampshire referee (who I am coaching and who is already involved with RFU Refs Dept development folks) last weekend do a L10 adult match - G's all through the assessor's reports and my only coaching notes involved tackler away / tackled player actions phases, set first line-outs using front man to mark a full metre gap, and dropping back to chariot from slow ball at scrums (he still plays at Colts level as a scrum half, so is automatically dropping for #8 pick and drive/pop pass :biggrin
. He is accompanied at every adult match he does by an assessor / mentor. He is in his second full season.
We did the same with two guys previously who started at 14/15 and did age group below as normal, then at 17 did same age and some adult matches (always mentored). One (PTC of this Forum) moved to Cambridge (education) and then London and became a L5 Group Ref mid 20s. The other did club youth and schools matches until 16 then transferred to London where his dad is an active Society referee (they live on Hampshire / Surrey border, and he went to St Mary's College in Teddington for HE) , and they quickly developed him at 17 to adult matches - at 21 he was on London Group at L5.
As a SW Group Assessor I have watched three of the SW Group squad this year who are in their early 20s (products of Gloucester Uni Referee scholarship course & Chris White's Officials Academy), and all did the start at 14 and work through year below age group, adult matches at 17 process.