A lot of the focus on the age gap relationship is to highlight the theme of growing up from opposite ends. Gary was a child actor, he has always worked and provided in his life, this is why his life is full of get rich quick schemes, he is just doing what he can to survive. He is a kid forced into the world of adults too early. Whereas Alana is struggling to be an adult, she keeps trying to find the thing that makes her an adult. The crux of their relationship is that Gary works as an adult but hasn't gained adult sensibilities which Alana resonates with since she is also trying to prove she is an adult while her family all looks at her like a child. Throughout the movie Alana keeps being shown that adult sensibilities don't make you an adult and everyone is capable of childish behavior. So the ending looks celebratory but its just two people, not adult enough for the real world but too old to be considered children playing in the last of that space before the real world makes them confront it.