PDR1
I think you are confusing the age at which flying lessons could begin with the age you had to be to go solo.
I did all my gliding in civilian clubs. I took my children flying from quite an early age -10 years onwards. They got used to gliding very quickly, and as soon as they could reach the rudder pedals I began to let them learn to fly. I don't recall any limitations on the age at which you could do this, The ATC probably picked 'nearly fourteen' as a good time to start introducing youngsters to flying. Did anyone ever go solo before sixteen?