What age is considered an adult or mature bird?

[Nakiska]

At what age are Cockatiels considered mature or adult birds? Is it the same for all birds? We also have a Conure who's just 3 months old...I know he's still a baby...but when do I have to start considering him a "big boy"

Thanks,

Toni

 

[antoinette]

This link below is very interesting, A to Z about Cockatiels
Cockatiel information, Lets Talk Birds