L.M.
Assuming this is a legit question...
I would have also not let him see my breasts but would have followed it up with a conversation. Why did he ask? Why did he want to see MY breasts? What have they covered in health class? Sounds like he's definately ready for the talk (if you haven't had it already)? Dad or another trusted adult might be best for some of it.
If it's not...please go away.