The story begins: "It was the summer of my fifteenth year." It's written first person/female.
My question, how old was she? My guess is that Lubrican intended us to believe that she was fourteen, because you presumably begin your fifteenth year immediately following the 14th anniversary of your birth date. Therefore, she won't be 15 until her next birthday.
But, as written, I would also guess that most readers would conclude she is 15.