Hello there! I have a tiel on top of my budgie flock, so I know a bit about them Allow me to digress...

1) At what age and where should you acquire your new cockatiel?

First things first, there are basically two ways to raise a human-tame chick. 1) Is human hand-feeding. This can be done multiple ways, but basically, the chick is taken away from its parents and raised on a man-made formula. This formula is then fed to the chick by a human, reinforcing the idea that "Humans = Your Friend and Caretaker". 2) Is the method that I use and prefer. The chick is NOT handfed, but raised by its parents. However, from around Day 10, the chick is continually socialized with humans through gentle cuddling. From this point on, these chicks are tame and generally very very friendly towards humans. *Generally*, quality, handfed/handtame cockatiels can only be found through private breeders. You can find a multitude of private breeders through Up At Six and BirdsNWays (sorry, you'll have to Google these sites).

Ideally, any age is OK to acquire a cockatiel. Think of a tiel like a dog. If you get it from a good, private breeder, you'll get a clean slate to start on. However, you could also adopt an unwanted cockatiel who'll take a little more time to "mold", but the rewards will be tenfold.

2) What should I feed my cockatiel?

I honestly don't remember the exact percentages, but I think it should be something like:
50% Pellets (Lafeber, Harrisons, Zupreem, KayTee, etc. brands)
35% Seeds
15% Veggies and Fruits (I like to have more veggies than fruits)
and you should always include the occasional yogurt treat, egg biscuit, eggfood, and various supplements from time to time.

A MUST: You should keep a continuous supply of cuttlefish bone and mineral block clipped to the cage.

3) How do I tame/train my cockatiel?

This is a very lengthy subject, so I'll leave this to Mattie Sue Athan
(I recommend this book for *every* first time bird owner)
http://search.barnesandnoble.com/boo...64110306&itm=2

4) What kind of cage should I buy for my cockatiel?

The biggest one! Just be sure the cage is NOT round or cylandrical and the bar width is small enough so that your cockatiel won't get his/her head stuck in it. Also avoid "guillotine" style doors which you'd find on virtually every cage in a store like PetSmart. AVOID cages like this (notice the sliding, "guillotine" door)
http://www.petsmart.com/global/produ...=1123996734053
Look for cages like this:
http://www.petsmart.com/global/produ...=1123996734052
Notice the clip to open the door

I don't remember the exact cage requirements, but make sure that you buy the largest cage you can afford. Generally, your cockatiel should be able to open his wings and his feathers should not touch the sides of the cage.

That should cover much of your questions. If not, PM me Good Luck!