Matthew Quick also said that the movie and the book are separate and that there was nothing wrong with her being cast.

And with American Hustle and Joy, Russell specifically wrote these characters for Jennifer. Literally nobody else was ever considered for either role. Rosalyn, in particular, would not have even worked as an older woman because the character is written from the bottom up as a childish, dependent, young mother. With Joy, he did the movie because he wanted to make something entirely for Jennifer. If he had not decided to make the movie, it would have been entirely different, and more of a biopic.

As for Jennifer's comments, she is speaking on the fact that the inspirations for these characters were older. The characters themselves, are obviously not, as they have been re-written. This happens literally all the time in the film industry, but nobody seems to care or even notice unless these two individuals are involved. Did you know that of all the acting Oscar nominees this year who played real people, roughly half of them were around ten years younger or older than their characters were at the time their films take place? Did you know that the film Steve Jobs is nearly identical to Joy in that, aside from Joy's prologue and epilogue, both films take place over the course of about fifteen years? Why is everyone except for Jennifer Lawrence allowed to play characters over the course of many years, and why is everyone else allowed to play characters "too old" for themselves, while she is criticized for playing characters specifically written as being her own age?

You're calling these "flaws" when, in actuality, they are simply preconceptions. What is the logic that makes these castings seem flawed to you? Is it because a woman in her early twenties cannot be married and lose her husband? Is it because a woman in her early twenties can't have a child at a young age and need to be rescued by an older man? Is it because a woman in her early twenties can't invent a mop?

Can I make a recommendation to you? Stop worrying about the inspirations for characters and worry about how the characters themselves are written. Going into a film with preconceived notions just causes you to find problems that aren't actually there.