On Australian football history
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National under-age tournaments have been held annually since the 1960s. The first tournament I've been able to track was the 1964 National Youth Carnival, an U18 competition played in Adelaide. A few years later the age group was changed to U16.
By 1970 it had expanded to U10, U12 and U16. The competition had also been rebranded the National Junior Championship for the two younger age groups with the older group the National Youth Championship.
A further expansion had U12, U13, U14, U15 and U16 teams playing by 1973. It appears the U12s ended in 1980 and for quite a few years the oldest age group flipped between U16, U18 and U19.
National Talent Identification Championship seem to have commenced in 1990 with U13, U14 and U15 only. Sydney, Newcastle, Melbourne, Brisbane, Adelaide, Perth, Canberra, Hobart, Darwin, the Gold Coast, Lismore, Morwell, Alice Springs, Bundaberg and Whyalla all hosted tournaments between 1964 and 1999.
By the 2000 edition the tournament had been slimmed to U15 and U16 with hosting rights held by Sydney. That changed around 2005 or 2006 to Coffs Harbour."
So sounds similar to other parts of our youth development, expanded in the 90s then slimmed down in the a league era, perhaps expanding again.