interesting point, my 13 y/o had 4 hours of lessons and got up and going, given all clear to practice what he's learnt before further lessons, then had a mishap that kept him out of the water for 8+ weeks, so got a bit rusty. the next couple of attempts were not real successful our local beach conditions not ideal, on shore shallow with close breaking waves. took trip away to a more beginner friendly location and he nailed it there or caught up. back at our local recently after some difficulty in getting going was sorted by shortening line length, still need to get working to windward together but handled the chop. the gear that the kite shop put together needs 15++ 7.5 M , we are lucky enough to be part of a small group that plays together share gear and advice, oli being the smallest has an advantage, has played with 15M, last man standing.
so after 20 odd hours on the water, looking at his own 12M kite and a 2nd larger board to give options on the day. it doesn't stop with lessons.
Lessons are important as is the people you play with.
P.s i'm a sailor not a kiter and oli has been land kiting from 10 y/o so probally had a head start. Pansh 4 line foil relatively cheap, though not on bar could help if you have not flown, before you line up a lesson.