I think that performance in the Juniors division is not necessarily an indication of where he will be 5 years from now. Look at the physical difference and speed from Juniors to the U23. Night and day. I saw this phenomena in track and field. Youngsters able to compete with adults at a younger age but as they got older, all that leveled out.
I see it in swimming all the time. Look at Michael Phelps, 16 at the olympics, etc. Most of us remember being in jr high or high school and comparing our skinny weakling bodies to the couple of guys in school that were Animals. All this 'hobby talk' is ***. even if people have only been racing for a couple of years were either at a high level in some other endurance sport or were cycling 'as a hobby'. At any age you have the fact of diminishing returns on extensive training, especially at that age.
Some people blossom early beyond their peers. Doping aside, Lance Armstrong was winning pro triathalons at 15. Then a Froome, from Kenya and South Africa that had None of the pipeline training others did. He went out and rode his bike. Didn't do well at the U23, etc. Now he's the best all around grand tour rider of the present generation. If this kid is doping, why didn't the other kids who are doping kick ass like him?