‘Being in love is the most difficult challenge of your life’: Paul Thomas Anderson and Alana Haim on making Licorice Pizza

The director's new film is a freewheeling romance starring two acting newcomers: the musician Alana Haim and Cooper (son of Philip Seymour) Hoffman. Anderson explains why their age gap matters, how they ripped up his rule book - and when he realised pitbulls were the best pets

I remember thinking as a kid: I can't wait till I grow up," says Paul Thomas Anderson. I can't wait till I get older and I can shed all this stuff, and all the answers will be there for me."

America's best director is now 51: salt-and-pepper hair, still as loose-limbed as a student. Those answers are yet to materialise, he says, grinning. No one sets you up for that. My dad never said: Oh, by the way, it's going to get a lot more complicated and a lot harder.' Or: Being in love and having a relationship is going to be the most difficult challenge of your life.' I don't know why. Maybe it was just my dad."