Its different for every girl. 9-13 would be the age range.. if you get them before hand talk to you doctor, same as if your 14-15 and you don't have boobs yet.
Girls develop breasts due to the hormones in their body. Usually, breasts are developed at the age of 10-13 They have different hormones to boys, which is why boys dont have breasts.
When you think you have developed breasts
A girl's breasts are usually fully developed by the late teens to 20s.
Gynecomastia
Wrestlers have well developed pectoralis major muscles. These muscle are placed behind the breasts. That makes the apparent size of the breasts look bigger.
Breasts developed on women for child bearing. Back in ancient times they didn't have bottles and formula for the babies.
The female secondary sex characteristics are enlarged breasts, developed clitoris, menstrual cycles. The visible one is the enlarged breasts.
It is likely that if big breasts run in your family, you will have big boobs also. However, it is also possible that women in your family developed big breasts only after giving birth (and didn't breastfeed). Ask your mother, sisters, grandmothers how and when they developed. Of course, genetics isn't fool-proof. You may just not have big boobs.
Once developed breasts will not get enlarged with creams and massages. Just be happy with what you have.
Answered your own question. It's genetics. You inherited from your mother.
For sagging breasts is recommended breast lift surgery or so called mastopexy. This is cosmetic correction procedure developed for sagging breasts. Usually it uses tissue from breast and fat to correct sagging skin.
Discharge is linked to puberty and not breast size. Discharge is what cleans the vagina.