There are fashions in writing, just as there are in clothes. The modern trend, particularly for genre or YA fiction, but increasingly in literary fiction too, is to start the story with the main character on the first page, and to start with the inciting incident. No backstory before chapter three, and then pare it to the bone. "YA" most likely stands for young adult. There hardly is a brand of monkeys that are stupider than young adults. Except YA writers. Give them a dildo and it will keep them occupied for hours.