If you're under 18 in the United States, you need written parental consent to get a piercing. This means that your older sibling would not be able to take you to get a piercing unless they had written parental consent from your parents. In some states, like New York, you also need to be accompanied by a parent or legal guardian when getting a piercing. So even if your older sibling had written parental consent, they would still need to bring along a parent or legal guardian in order to sign the consent form and accompany you during the procedure.