I am a grown man and feel guilt over my arousal. I find myself very aroused when looking at say a National Geographic picture of nude females. I know this is common however I find myself really aroused at the site of girls who are obviously underage. I really find images of young girls breasts beginning to bud and other girls who are little later stage of development so beautiful. I cant explain it. I have no attraction with their clothes on, only when I am exposed to their nudity by some means like Nat geo. It is easy to find nat geo type of material on the Internet. I have noticed that I immediately have sexual arousal when exposed to this. I have dozens of pictures that I look at and feel the shame. I obviously hide the pics with some regular porn I have. I dont have guilt about the porn but I do about the other pictures that arent meant to be.
Don't be ashamed. All of us get "turned on" by something and that is yours. Others porn, being naked, feeling sexy. And yours is ok