being a parrot owner, one thing that amazes a lot of people is that many birds, like my cockatoo, will grow to just about full size in the first 9 months of their lives. The smaller birds don't live as long as the larger ones usually do, but in captivity their life span can nearly double. My cockatoo can live to be 60+ years old, the oldest one I know of lived to be about 72.
And you should see a cockatoo baby...they look like little ugly pink pin cushions!