This is why I think stereotypes against teenage mothers need to stop. Do you agree?

My friend who is 26 years old, but looks really young for her age, just had her first child. While she was in the mall and snotty old lady told her she was too young to have children and she replied how old do I need to be. And the woman said atleast 20, and my friend replied that she was well above 20 and that she needs to mind her own business and walked away. How do we account for those woman who look young, when there is a chance they look older then they are.