First of all, it's not even clear if Aiden is really 17!
Secondly, Aiden is a high school bully with some connections to gang members who's got a powerful uncle. Nothing more. He's neither Richard Ramirez, nor Ted Bundy, nor Ed Gein, nor Jeffrey Dahmer, nor Charles Manson! So calm the fuck down! Yeah, I know that their victims also didn't know that they are serial killers. But you definitely misinterpret and overinterpret Aiden's role and the role of a bully in general!
Thirdly. What exactly would Aiden get out of it if he'd cause harm to Sophia? What would he win with that? He's also not a complete stranger to Sophia. He's just trying to see how far he can go with her. So, raping her in the forest would be pretty counterproductive plus neither Aiden nor any of his friends is a fucking rapist! Are you serious? Plus you don't even know what they're talking about before the drive!
Last but not least. You have the god damn option not to drive with him and put your son to the boarding school. If you think this is more realistic, do that! Nobody's forcing you to drive with Aiden nor to do his tasks! If you think incest is unrealistic. Don't go with it! Just play the good wife route and enjoy your realistic gameplay!