Tell a parent (do not be embarrassed). Then go and see your GP. At your age, i highly doubt it's anything, but if you're worried enough to be posting on here, it means it's affecting you mentally already.
My wife was diagnosed last year, and our daughter is ages with you. We have told her, what I'm telling you through bitter experience. It's always better to get anything odd seen to. You're probably just going through development. But don't take the word of some internet random, get told that from someone who can examine you.
Inverted nipples are quite common. Because you're young you may find that over time this will go. It is normal and is not usually related to cancer. Also breast cancer at your age is nearly unheard off.
Because you are worried, I think the best thing to do is talk with a trusted adult about this and if there is a concern do go and make a GP appointment to get checked out.
You may also want to read what another charity called Breast Cancer Now say about teenagers breasts and this includes specific information about inverted nipples, you can see it here
I hope you will be okay.
Please get back to us if you need any more information or support. You may find it helpful to talk things through with one of the nurses on our helpline. The number to call is Freephone 0808 800 4040 and the lines are open from 9am till 5pm Monday to Friday.
Do read what Nurse Caroline said. Inverted nipples can be common and the majority will go back to normal and you say that both your nipples come out when you take your shirt off so I don't think you need to worry too much.
If this is something that is concerning you then do discuss it with a trusted adult or make an appointment with your GP so they can help reassure you.
I hope this helps and you can stop worrying about them.
