Hi,
Cockatiels get their adult feathers & colors by the time they are about a year old, and once that happens, there is no way to tell how old the bird is. You can send pictures to me at [email protected] and I can let you know their sex depending on what color mutations they are. Be sure to put my name in the subject line. Cockatiels should be at least 2 years old before you let them breed. Some minor quarreling is normal whether they are a pair or not. As long as they are not pulling feathers out of each other or drawing blood, it’s OK. But not all birds will be compatible or be good breeders. They choose their own mates in the wild, and do not always like the mate we choose for them. My main concern with these 2 birds is that they might be related. Did you ask the shop keeper? You should never breed related birds, so if these are brother and sister, they need to be separated. I’ll wait to see the photos and let you know what I think.
Thank you for asking Lafeber,
Brenda