36 B is an average size, neither large nor small. 34B, 36B, 34C and 36C are the four best selling bra sizes out there -which means that your size is average. In reality there's no such thing as "average" or "normal" or "too big" or "too small". Many things beyond age and height determine breast and bra size including hormones, genetics, fat distribution and body fat percentages. Additionally your bra and breast size changes throughout your life. What you take now is not the size you will take in two years, or five years or ten years. Bra and breast size will change all your life. So there's no such thing as "average" no matter what your age is.
Since there's really no such thing as "average" or "normal" embrace what you have an don't waste a single second of your life worrying about size. Simply buy the bra that fits and feels comfortable and ignore the numbers and letters. Fit and comfort are what's important. Not the size.