If they play Triton’s backstory as him being the son of the sea god Posiedon, which was what the original myth was in greek mythology, the womanizing would make more sense. He would be a god himself and well the greek gods weren’t exactly the most faithful men in the world. As far as the Little Mermaid goes we never actually got to hear Triton’s background story or what happened to make Ursula so mad at him. As for age well, gods can take on any form they like..so he could appear to be whatever age he liked..