What happens when using vitamins meant for adults?? (READ DETAILS BEFORE ANSWERING!!)?

To be honest, I don't see anything in that list that would be bad for you. The dosage would have to be cut for a 13 year old, particularly if you had a smaller or slender body. Instead of taking 3 capsules per day, you should be just fine if you limit it to 1 capsule per day. Take with food. There's nothing in there that's going to hurt you if you only take 1 capsule per day.