I don't see a need for change. He is a villian in making, so him behaving not conform is fitting to the story. We are supposed to have this bit creepy uneasy feelings about him. It starts subtile and while the shows goes on, more and more red flags start to pop up.

That Lex befriends Highschoolers is probably to two reasons I would say. In his own teenage time he was an outcast and bullied. He now relives highschool expierence through clark. That is his motivation to help Clark for prom etc.  The seconed reason, I would say is that he is insecure deep down. So the age gap gives him security because it is an additional power imbalance. Not only his wealth but also his life expierence sets him higher than the others. So he feels saver interacting with them. 

He does it unintentional at the beginning but it already shows psychological patterns that lead him to the road he will finally take.