I Need to know!!!

Hi, I'm 15 years old, and this might be really common but I'm afraid my boobs aren't going to get any bigger. They're probably a med-side A cup now, but have gotten WAY smaller since I've started working out. They don't feel firm (and I heard that firmness means they're still growing). I'm having a little bit of self confidence issues, so I want to know when is the normal age for someone's breasts to stop growing? When did yours stop? Thank you!