I really don't think the planet is a training ground for juveniles. If anything, it's the opposite.
Other predator hunts have taken place on earth, or wherever, and the predator has gone to the hunting grounds. They actively go out and hunt for prey in the prey's own territory.
The 'super' predators are like rich, crass, 'sport' hunters who own their own island, and have the game shipped in, so that they're hunting in their own territory instead. Stacks the odds in their favour.
The wolves comment also works with this. Dogs and wolves are equally as dangerous, but typically, a person would be more inclined to approach a dog, right? Might not mean that the 'super' predators are more powerful, or more dangerous than a normal one, just that they're meaner. (I do realise that the concept of wolves being mean is kinda silly, and anthropomorphic, but I'm looking at it from a general and literal audience perspective.)
At the end of the movie, more prey is airdropped in, presumably by other super predators, although it may be automated or something, we don't know. The hunt begins again, except it's not a real hunt. It's all staged and stacked in their favour. They don't even bother going out to hunt for prey, it's all brought to them. They're lazy. Maybe they're rich? Since it's been said that The Predator is set before Predators, then it could be that they're the result of genetic modification.
If there's some sort of predator economy, then maybe the super predators are the rich ones that own their own preserve, can afford to upgrade themselves genetically, and are lazy enough that they can't be bothered to honour and hunt, and instead they have it brought in. They're also mean enough to torture and kill the jungle hunter that isn't one of the elite.
So, probably not juveniles.