I am thinking of doing ear piercing for my 18m girl. Should I do it now or when she is older?

I think you should do it now. She won't remember the pain when she's growing up neither would she be afraid. I still remember bringing my daughter to get her ears pierced when she was 6 years old. She was so afraid and after getting her years pierced, she kept crying! To coax her, I brought her for some really good ice cream! :-)