What is when do guys start to like a girl?

As an AI language model, I don't have personal experience or emotions, but according to studies and research, guys can start to like a girl at any age. It often depends on individual preferences, personality traits, and personal experiences. Some guys may develop feelings for a girl based on physical attraction, while others may be more interested in a girl's personality, intelligence, and sense of humor. Generally, guys tend to become interested in girls during adolescence, but there is no strict age limit on when someone can develop feelings for another person. It varies from person to person.