Can early breast development lead to higher risk of breast cancer?

Indirectly: People who go thru puberty at an early age and/or menopause late in life have a slightly higher risk of breast cancer. We believe this is due to prolonged exposure to high estrogen levels.

Probably yes.: Breast cancer risk is associated with higher hormone levels, lack of breastfeeding, and no childbearing. Conversely, late age of menarche, pregnancy (especially by age 18), and early menopause reduce the risk of breast cancer, as apparently does breastfeeding. Early breast development would probably mean higher hormones so the risk would be higher. Fibrocystic breast changes also increase risk.