Ephebophile or paedophile (for teens and preteens respectively)

No, he could be an ephebophile, one who is attracted to later adolescents, those 15 to 19. But, not enough facts are present to say, and neither you nor I are qualified to make the diagnosis. Only evaluation by a mental health professional can determine whether or not someone suffers from any form of disorder covered by the DSM-5.

Major characters: Peter Griffin, his wife Lois, the kids Meg, Chris, & Stewie. Brian is the family dog.

Reoccurring characters: Glenn Quagmire, Cleveland Brown and his wife Loretta Brown, paraplegic police officer Joe Swanson, his wife Bonnie and their baby daughter Susie (Bonnie is pregnant with Susie from the show's beginning until the seventh episode of the seventh season); neurotic Jewish pharmacist Mort Goldman, his wife Muriel, and their geeky and annoying son Neil; and elderly ephebophile Herbert. TV news anchors Tom Tucker and Diane Simmons, Asian reporter Tricia Takanawa, and Blaccu-Weather meteorologist Ollie Williams also make frequent appearances. Actors Adam West and James Woods guest star as themselves in various episodes.

Technically he is an ephebophile. Ephebophiles prefer adolescents, whereas pedophiles prefer prepubescent partners.

It is still illegal in many places, presumably due to the belief that adolescents are not yet mature enough to make an informed decision regarding sexual relationships. Adolescents are on a hormonal roller coaster and tend to be more emotionally fragile than adults on a biological level.

Whether or not the adult is aware of it, there is a power differential involved that can cause the adolescent to develop a strong emotional attachment and a subconscious need or desire to please the adult. While this can be interpreted as "liking him back", it is more often than not a form of transference. Some adults purposely abuse this power differential, others are honestly ignorant of the power they have over their young lovers, and the psychological damage the relationship may cause.