I say it is all a personal decision. Although I had a TIEL when I got my SUN, at a little over a year old, and the TIEL passed before my TAG came into our lives, at 3 months. Then the TIEL I have now came a few years later. I am one of the lucky ones in that the TAG and SUN can be out of cage at the same time and do fairly well with each other. If they were to fight I would be at a loss as to how to give them enough out of cage time. They will even sit on my shoulders and wait their turn when I hand out treats - it is too cute! When the TAG was little, he taught the SUN how to play with toys! Enough rambling. Take in to consideration your time, energy and room in the home, BEFORE you think about if your Grey would like a friend!