[Satan]

Homosexuality was( and is ) considered a mental disorder for many years.

How is being attracted to a different age different then your sexuality? I guarantee you have a type that has an age component, and surely a maturity component.

Sexuality as referenced here is used in place of sexual orientation (homosexuality, contrasted from heterosexuality and bisexuality), which deals with genders.
If you're going to consider pedophilia, which is as it says, a philia, "an abnormal liking for or tendency towards a given thing" as that is defined, a orientation, then you must also include every single other philia in the world as a orientation.

"Research has shown that homosexuality is an example of a normal and natural variation in human sexuality and is not in and of itself a source of negative psychological effects"

Homosexuality is not considered a mental disorder except by those who hold firm to that belief ignoring research into its cause.
It causes no more harm than a heterosexual relationship given the same scenario and setting.
You cannot say the same about pedophilia. Pedophilia creates a victim, and is shown by research to have a negative effect in general on both the victim and the abuser.

EDIT:
Per your "homosexuality was (and is) considered a mental disorder" comment, Can you post a statement supporting that from a reputable source, the American Psychological Association says otherwise.
http://www.apa.org/helpcenter/sexual-orientation.aspx

While I can't find a online copy of the DSM-V to quote the direct line from (Probably since doing so would possibly be piracy), the American Psychiatric Association is quoted on having fixed the definition in DSM-V from an erroneous one.

"In fact, APA considers pedophilic disorder a ‘paraphilia,’ not a ‘sexual orientation.’ This error will be corrected in the electronic version of DSM-5 and the next printing of the manual"