Fibroadenomas are less common in women your age, but, still possible, especially when the woman receive estrogen therapy.
They can cause pain, when growing large (more than three cm) and surgical removal is usually recommended.
MRI or biopsy are used when the ultrasound can't distinguish and diagnose a fibroadenoma or other type of breast lump.
Biopsy or excision of the lump is important (do not accept watchful waiting)
Best wishes!
Marija