I think the biggest reason in the pokemon world why ten year olds are able to become champions and dismantle criminal empires is simply because kids are both reckless and really sweet. Like most adults or older teens becoming trainers would be like “oh fuck oh shit, that’s a deino I can’t handle a dragon type yet i need to run” while a ten year old would look at this dude,

and think 

“!!!! WEIRD DOG!! I LOVE YOU!” 

and would run over to hug the incredibly dangerous dragon, that bites everything it can find, only to be left completely unharmed because this is the first time this dragon felt loved. 

And they would be able to instantly tame them, because kids can be REALLY protective of animals, so they would just braid up the deinos hair so they can see, and bring them to a pokecenter to heal them. 

And because this deino can see now, it’s fur isn’t going to be stained with it’s own blood (thats the red spots on it’s mane) And would adore this kid for everything they’ve done.

And heres another thing, with adults and teenagers becoming trainers, especially ones in criminal empires, they would likely want only really strong pokemon, and wouldn’t have the patience to raise a pokemon thats not going to be strong for a long time. They would just buy a machamp or something.

But kids wouldn’t care about that, they’d just pick pokemon they thought were cool and become friends with them. So because this kid, who doesn’t know about dangerous pokemon, or cares about their weird dog being able to take down a gyarados, they would likely be some of the only trainers with enough patience and care to raise an unbreakable bond with their pokemon, until their “weird dog” evolves into a fucking flying hydra known for being capable of mass destruction and decimating villages without problem.

and not only that, but at this point they would have bonded so strongly with their “weird dog” that this near godlike being capable of mass destruction is completely under this 10 year olds command because of how caring they were.

Imagine having a dragon as your friend who’s just like “YOU KNOW HOW MUCH I LOVE THIS KID? MY TRAINERS THE FUCKING BEST. I CAN’T TELL YOU HOW MUCH PAIN I WAS IN FROM THE DENSE FUR COVERING MY EYES, FORCING ME TO BITE EVERYTHING NEARBY INSTEAD OF SIGHT, AND WHEN WE FIRST MET? THEY GAVE ME A HUG, BRAIDED MY HAIR, MADE ME CURRY, AND TREATED MY WOUNDS. IF ANYTHING HAPPENED TO THEM, I WOULD DESTROY THIS ENTIRE REGION TO BRING THEM BACK.”

so thats probably why children are constantly defeating top tier criminal organizations who are after godlike beings that they almost always end up forcing under their control, failing, and having to deal with an angry god fighting them, only for the same 10 year old to be like “OH MY GOD!! GIANT WEIRD DOG!”