Why are my cockatiel's tail feathers broken?

If he is clipped I ask if he lands on his butt when he tries to fly?

At least he will be going into a molt very soon and most of the damaged tail feathers will be replaced.

Young Tiels are very clumsy any way, so it is possible that he is just a normal young one. The clipping will not be helping though.

Hopefully you will not be clipping a flighted animal again. Birds are meant to fly. And they need to do this to get a full cardiovascular work out to stay healthy and live a full long life.

Added notes:

Thank you for the extra info.

As the molt coming up is his first, so will be when he changes from junior to adult plumage and so will molt out almost all his feathers. they also become more aware of looking after their feathers after this. But the clipping may mean he still butt lands if he tries to fly. So try to not scare him into flight.

Clipped feathers do not regrow and will only be replaced as he molts them out.

Plucking can be done and tail feathers are easy to pull as they are by nature designed to come out easy. This is due to them being caught by the tail by prey, which leaves them with just a mouth full of feathers if the bird is lucky.

that is a bad option, if their wings are trimmed it may grow back slowly, very slowly, but the tail will not, even in molting season. you should pluck the tail feathers out by an eyebrow plucker, I have done the same to my birds. whenever they have broken tail feathers it will not grow back because it has strong roots.you have to pluck them out. try to take them out one by one, fast and swiftly to reduce the pain and not make him bleed. it must be taken out from the root. if you are not experienced, ask an expert for help. long tail helps the bird fly and balance itself.

Birds molt, they slowly lose all their feather around twice a year, so his tail feathers will indeed grow back. As long as there is no blood, he is fine.