"One of the things I would like to do is make up stories that I would have enjoyed when I was a kid. So, if I'm thinking about an audience, it's usually a younger version of myself"

Matt Groening is expressing his desire to create stories that he would have delighted in as a kid. He is suggesting that when he is producing stories, he is thinking about a more youthful version of himself as the audience. This implies that he is creating stories that he thinks would have resonated with him as a kid, and that he is producing stories that he thinks would have been pleasurable for him in his youth. He is likely attempting to create stories that are entertaining, creative, and meaningful, as he believes these are the kinds of stories that he would have appreciated as a child. By developing stories that he thinks would have been enjoyable for him as a child, he is most likely attempting to create stories that will be enjoyable for other kids too.