There's no set rule on when to start regular appointments. Usually I've heard age 18 OR when sexual activity starts, whichever comes first. Sometimes it's earlier than 18 for other reasons, for example "female problems" in the family.

Whenever it is, I would suggest taking an older woman you really trust with you. For my first one it was just me, the doctor, and a nurse who was required to be there for liability reasons. I really respected both the doctor and the nurse so it was all right, but it could have been better if someone I trusted would have been in the waiting room when I was done.