van Gogh’s painting “The Starry Night”.
the “good old day”--> I think it should be "days".
Gil Penter, the protagonist of the movie, is a Hollywood screenwriter who idolizes Hemingway, Fitzgerald, and many other great writers and artists in the 1920s. --> not completely sure, but I would remove the "the" before "protaganist". "in the 1920s", I would use "from the 1920s".
which makes him realize that it is an illusion to think that the past is better than the present, and that he must get rid of this myth about the past in order to become a good writer..--> a little unclear whether the third "that" is parallel to the first "that" or the second one. maybe start a new sentence.
I am sure that our era may someday become a: to me "am sure" and "may" kind of contradict each other a little bit.