"It would have been nice for Greg to eventually grow into a mature relationship with Laura. He was moving toward that already but then took a turn into the juvenile with Paige"

This quote recommends that Greg and Laura had a relationship that was not mature. Greg was making progress in growing the relationship, but then he chose to pursue a relationship with Paige, which was more juvenile in nature. It implies that Greg was not prepared to take the relationship with Laura to the next level, and instead chose to return to a more immature relationship. It is possible that Greg was not prepared to dedicate to Laura, or that he was not fully grown enough to handle the obligation of a more serious relationship. It is also possible that he was not ready to let go of his more juvenile methods and accept a more mature relationship. Whatever the reason, it is clear that Greg picked to take an action back and pursue a more juvenile relationship with Paige.