I got both my daughters done about 5 years old, I think. Both did end up getting minor infections, as no matter how much you clean them at that age all they want to do is play with them.

My SIL had her baby girl's ears pierced at 6 months, she doesn't touch them at all and they have not had any problems.

It is totally your decision, there are pros and cons for both younger and older, and you need to weigh them up and make the decision thta is right for you and your baby girl.