It is almost as if asking a young woman how old they are is habit in America.  One of the reasons they ask is because they can get in legal trouble if a man over 18 talks to (usually female) minors under 18.  It is a common question in America, and another reason a person might ask is usually if they find you interesting, even just as friends.  Women ask these questions too,  age can be a casual discussion such as hobbies, favorite subjects etc.  Age helps you know the person.

New friends

I went to the beach, and while I was swimming I did not see that a boy had seen me. Later, when I went with my mom to the other site of beach, the same boy came closer to me and said "hello."  We talked for a good time while my mom was exercising. He was with his friend, and he introduced me. They practice surfing, so I hope it will only be a few weeks  until I learn a new sport.
It was a good morning, and I made two friends.