Why is my puppy so aggressive?

Hopefully, it's not true aggression that this question would be geared towards. I have seen puppies that are aggressive at a very early age and that's a little bit disturbing. More times than not, it's just playing. They're trying to find themselves in the pack. They're trying to find out who's the alpha and who’s not. What can they get away with? They're learning how to interact with dogs. And if you've ever watched a pack of dogs, wolves, any canine species, that's how they are. It's what they do. So the playfulness/aggressiveness is okay for them to do those things in moderation, as long as it's in play.
If it becomes growling, snarling, pulling, and as if they have to have the last word, that's a problem, and that needs to be addressed straight away. I'm not a trainer so I'm not going to stand here and try to give you this long, drawn out process on how to do it.
But one thing you might want to do is consult with a trainer and see the right methodology on how to break that or steer that energy elsewhere to where it becomes productive and not leading down a not so good road.

Puppies are more playful than aggressive. It just may come across that way because they're growling, biting, chewing, and wrestling. And that's how they grew up playing with their littermates. And unfortunately, sometimes that comes off as aggressive to their owners, but mostly they’re just being puppies.