My daughter didn't get her ears pierced until her 7th birthday and it will be the same for her little sisters. My reasons are multiple. I had an allergic reaction to the metal of the earrings I was pierced with as a child and I don't want to risk my babies going through that until they are old enough to verbalize to me that something is wrong. I also want them to be old enough to take care of them hygienically by themselves.
She was about 8-9 months when we had it done. We went to a place that specializes in doing babies ears, not the inexpensive shop in the mall. Two people did it so both ears were done at the same time. They had/used solid gold earrings to pierce. They would not do it from after her first bithday until 2 1/2 because of the risk of her 'playing' with them causing an infection or injuring herself by pulling on them.
We had our daughters done at 4 months after her second round of shots. I had mine done at 3 weeks and never had issues with that piercing, I've tried getting a couple more since then and have had nothing but trouble. My daughter literally whimpered for 15-20 seconds and then was back to smiling at the lady who did it.
It's one of thow personal choice thing what has no right answers. Our doctor said wait for the second round of shots and we did for our first girl. For our second it ends up a first birthday thing just because it worked out that way.