When Do Thirty-year-olds Get To Be Women? Not when they're The Girl On The Train

At the pool yesterday, racing between children-- (I'm one of those uncool moms who swims and laughs a lot and drags them through the waterfalls)--I saw a woman reading a book called The Girl On The Train. 

I knew nothing about this book, but as I dripped my way from one child to another and one pool to another, I thought--The Girl. The Girl. How old is she? Ten? A teenager? What is she doing on the train, this little girl, this teenager? 
But something told me the girl on the train was, in fact, a woman. 

On the way back, I asked the woman what the book was about. "Oh, she said, there's this girl and she rides this train everyday and she gets really interested in this couple that she sees from the window. Like she almost thinks she knows them, but she doesn't. And then, the wife in the couple disappears, and she starts to worry about them." 

"How old is this girl?" I asked. 

"Oh, twenty-nine. Or in her early thirties." 

"Thanks," I said. A woman, then. A woman on the train. Why isn't that the title? If it was a thirty-year-old guy would the title be The Boy on the Train? No. Why isn't it The Woman on the Train? Because we are more interested in Girls? What's wrong with women? Aren't they interesting? 

This is nothing against the book or Paula Hawkins, who may not have even had the choice of title. But really. Twenty-nine or in her early thirties, and she's a Girl? On the Train. Guh.