They may also feel heavier, or be sensitive. Without gaining this weight, you cannot grow taller, develop breasts, or get your first period. Wearing a bra or not is your choice. Remember that one side usually buds first as a hard, sometimes tender, knot under the areola. Although your breasts may still be growing and changing, it is a good idea to get to know how they teen age girl boob and look so you know what is normal for you. So when you think she's ready be on her side teen age girl boob always help her when she isaw upset about the ways she looks or feels.