I have a lump in my breast about the size of a golf ball its really hard and visible too. Im only 13 what is it? I have had this for a long time.

If its not a birth mark/defect then you probably need to get to the Doctors. Has the dr even seen it? Or your mom?

Most likely it's your breasts developing and it would be called a breast bud.

Show it to your Mom.

I was thinking that too but she said a rather than two (?) although at first I guess one could 'appear' before the other?
Plus long time --years ? Months?

I was thinking that too but she said a rather than two (?) although at first I guess one could 'appear' before the other?
Plus long time --years ? months?

Yes its only one, and I have had this at least since the beginning of this year so months. It has also got a lot bigger over time.

Since it is only one and it is getting bigger I would ask your dr. If it is symmetrically around your nipple it may just be your breast developing before the other one as J9 said.