At an annual flying school held near Hobbiton 16 yr olds are taken from 0hrs to about 8hrs in 2 weeks... most (not all, probably 90%) go solo in that time. The differences here are probably: quality, close supervision of less experienced instructors; total immersion environment dedicated to the students; "tried and true" syllabus and lesson plans; young minds eager to learn; early intervention when issues are identified.