Why does the human papilloma virus target girls between 9 and 13 years old?

It doesn't: Genital infections with human papillomavirus (HPV) are sexually acquired; the virus doesn't "target" anybody until and unless they start to have intercourse. The HPV vaccines are recommended in people age 9-13 to be sure they are protected when they start to have sex, which often begins at age 14-18. In addition, the vaccine is most potent and maybe most effective at age 9-13.