There are trends in book titles as in most things. There was a time long ago when a book's title could take up an entire page. Some old books might have two titles, separated by the word or. Much more recently, one-word titles became popular. We had Jaws, Coma, Topaz and the like.
A recent visit to a bookstore alerted me to the fact that the current trend is for novels to have the word girl in the title, possibly replacing the trend of novels with the word daughter in the title. About a decade ago I wrote a newspaper column that listed scores of daughter novels, and it was an incomplete list.
Now one can find The Girl Before, Luckiest Girl Alive, Copygirl, Hemingway's Girl, The House Girl, The Silent Girls, The Perfect Girl, Girl in Translation, Pretty Girls, Sad Girls, Lilac Girls, The Girl Who Came Home, The Painted Girls, The Girl in the Glass, The Girl in the Castle, Vinegar Girl, The Tea Girl of Hummingbird Lane, Small Town Girl, The Girls, The Forgotten Girls, The Girl You Left Behind, The Girl From the Train, The Girls in the Garden, The Girl in the Glass, Silver Girl, All the Summer Girls, All the Pretty Girls and The Wicked Girls.
Many of these girls seem to be in peril: Girl Waits with Gun, Girl in Pieces, Girl on Ice and The Burning Girl.
I found just one such book among the teen titles: Weregirl. So most of these novels were written for adults, and most of them were written by women for women, and most of the title characters presumably are women, never mind the girls in the titles. And never mind all the scolding men have endured for referring to anyone over 18 as a girl.
Even more than the word daughter, the word girl in a title, suggests youth. Readers, like moviegoers, seem to prefer stories about young women. Old women can find themselves in perilous situations, but you rarely find novels or movies about them. A novel called The Old Lady on the Train or The Forgotten Middle-Aged Women probably wouldn't sell very well.