What age do boys start thinking about girls?

9 to 10. I know alot of guys who had their first "girlfriend" if thats what you want to call it, when they were in 5th grade.

As a liking it can start as young as 3-5, but don't really understand liking a girl until they're a bit older 9-10. Sexually it doesn't start until puberty hits and hormones take charge. Which can start anywhere from 12-13.