I don't need to justify it. Our biology dictates that we will regularly find 15 year old girls attractive and it's only natural as they are developing their sexuality and entering the most fertile period of their life. We just don't act on it as it is improper in our society. Attraction is biological, but whether you choose to act or not is generally sociological and healthy males will tend to transfer any sexual feelings to those of a protector. In short, we might look at a 15 year old and think they're attractive, but will not be willing to act if the opportunity arose.