I'm 13, I have a large forehead, I was researching hairline lowering, but I don't know if I'm old enough. Any suggestion?

Hairline lowering is a routine part of my practice and is intended for patients like you who were born with a high hairline.  I didn't see any mention of hair loss in your paragraph, so I'm not sure what patient the other doctor is referring to.  There are no studies that show hairline lowering is the wrong thing to do for young patients, but I wait until age 16 for a variety of reasons.  Even at age 16, you will need consent from a parent/guardian.  You should continue to research hairline lowering and then seek consulation when you get a little older.

You need to have permission and consent from your parent or legal guardian before having surgery.  If you are mature enough to understand self esteem or happiness does not come from cosmetic surgery, your next obstacle would be getting your parent's permission.

At 13 you are too young to address the hair loss with any type of surgery. You need to wait to at least 18 of you are a female and if you are a male, maybe never because of the risk of genetic balding that occurs in 50% of men.