I personally dont feel it is normal or appropriate. You need to get parental controls on your computer which will make it so he cannot look at naked girls if he tried searching it. Id explain to him that he is too young and he should not be looking at things like that. Also it could be that some of his friends have talked about seeing naked girls or are infatuated with the idea and maybe they got a hold of someones playboy magazine. This happened with my 7 yr old cousin, his mom found him and a few of his friends looking at one. Not good! Expain it calmly to him since he is probably just curious but tell him it is not right to do. Good luck!
Yes not good online doing that... have you no Block on it perhaps not allow him free access to it .,some may consider it is normal well it may be that but its not good to encourage or allow it, does anyone else in the family go to these sites.