First of all he is entering puberty, it may or may not be precocious puberty, if it is threre is nothing you can do about it anyways.
I have to tell you it is weird your still seeing him nude, he is 7 and should be showing some standard of modesty by now. Hopefully your not still bathing a 7 yr old? You can search the subject mate, going to a doctor sound pretty lame to me.
Oops, forgot to include the link! Description of "partial" precocious puberty, if he's showing no other signs than just pubic hair.
http://kidshealth.org/parent/medical/sexual/precocious.html
No, that's not typical. You will want to ask his pediatrician about this - 9 years old is about the earliest age for onset of puberty in boys that's considered typical.