DH and others:
Thoughts are not acts but could lead to them if inhibitions break down. A person may admire a particular car or painting. Even thinking about how they would enjoy it if they owned it. But it is a long way from admiration to stealing.
The dynamics of being sexually turned on at a particular age via abuse is often a way that somebody gets fixated for a particular age range or (though heterosexual in orientation), may be attracted to penises).
Most people without premature sexual experiences get aroused to males or females around the time of puberty. When a boy who is heterosexually oriented gets turned on with sexual thoughts and feelings and discovers masturbation, what do they masturbate to? Usually, girls of 13 or 14 who are classmates or those "much older" women like 19 to 24 in Playboy magazines (at least in my case pre-pornography). We reinforce the thoughts and feelings of those young girls through pleasurable masturbation.
The dynamic of abuse which might disrupt a boy's development socially (he becomes shy, feeling different from his peers) and misses out social experiences and perhaps in HD's case, becomes older and older with the social immaturity below his numerical age.
The At Risk forum which his private, by request and invitation only, is a place where members can discuss thoughts and feelings that might be shocking or offensive to others. If a person is not comfortable about sharing thoughts of inappropriate activities or attractions (and there are people who are offended by admissions of those thoughts around here), they should consider the At Risk forum.
All it takes is having a paid membership in MS and a pm to me requesting admission. I will ask you basically what issues you are dealing with to be sure that the forum is the right place to be.
And, HD, I agree with those saying you should be dealing with this with your therapist who can hopefully help you with developing the skills to be more comfortable with age-appropriate potential partners.