LONDON—Dylan Penn, daughter of Hollywood heavyweights Sean Penn and Robin Wright, says she initially turned down the chance to star in her father’s new film “Flag Day”—her first major movie role—but its lengthy production let her mature into the part. Based on Jennifer Vogel’s memoir “Flim-Flam Man,” the film centres around her relationship with her father John, a petty criminal turned counterfeiter. Penn first read Vogel’s book as a teenager and at the time firmly rejected her father’s offer of the lead role. “He asked me when I was around 15, 16, and I solidly said ‘no’. I never thought I wanted to act and I just felt like I was too young,” Penn, now 30, said. “And then, 15 years later, I think after having real life experience I felt like ‘OK, I can draw from my life, reference my experiences and maybe color this character a little bit …