For me I did my daughter's ears at 13 months. I wanted to wait until her lobes had a chance to grow a bit. I have seen a few cases where you see girls and their earrings look like they are mid-lobe. She is now 11 and hers look perfectly placed.
I do have a tip: If you are going with a salon that uses guns and not needles (I suggest the guns for the babes) make sure they have 2 guns and 2 people to do it at the same time. It is much worse when you do one at a time. If you wait until she is older than 6 months like I did, take a sucker or something for her to have to stop the crying after. (and there will be crying)
The way I saw it when I did it was there was no way anyone could question whether or not she was a boy or a girl when she was small. I am happy I did it, but some people may find it is not for them. Good Luck with your decision.
Allie