What is the problem of them flying to the top of the cage? If we know what is going on we may be able to help solve that problem or maybe help you see if it really is a problem. Wing clipping is not always the solution.
You can clip whenever you wish but there can be issues. If the feather is still growing it will bleed. Clip only one at a time, look for blood in the feather before you clip. If you do clip one that bleeds study it and learn to recognize that it is still growing before you clip another one. Just because one feather bleeds doesn't mean they all will. They grow individually, often spaced out some.
Chickens go through a few juvenile molts as they grow. They outgrow their feathers and need to replace them. An adult chicken would look really silly if it still had the feathers it had when it was five weeks old. After each molt you need to clip them again.
Again, what is going on? Why is this a problem? Usually there are much better solutions than wing clipping, but in some conditions it will be the right thing to do.
[/.
I know they're birds and it's natural for them to fly. Sneaky buggers tho will wait behind the door as soon as I enter they will try fly over or on-top of the fence

not that I want to clip them was just wondering an age as I'd rather not have them fly over and get eating by a cat or dog