If you ask Judd Apatow, whose films have taken more than $2 billion at the box office worldwide, he'll tell you he's still just a massive fanboy at heart.

"Growing up, I just wanted to be Eddie Murphy, and I still want to be Eddie Murphy," Apatow laughs down the line from Hawaii where he is holidaying with wife, actress Leslie Mann, and two daughters.

Apatow, 47, has made a career out of writing about likeable, flawed people with good intentions, who occasionally get lost along the way. In recent years, the filmmaker behind The 40-Year-old-Virgin, Knocked Up, Funny People and This Is 40 has helped others do that, too.

Apatow's love of comedy ("These people were like superheroes to me") came out of a turbulent childhood. His parents' "toxic" relationship dragged on for many years before they finally divorced.

"I felt very alone in high school because no one was interested in what I was interested in," says Apatow, who grew up on Long Island in New York. "I was the kid in the library looking up old articles on Lenny Bruce."

At 15, Apatow started interviewing comedians for his high school radio show, convincing stars such as Jerry Seinfeld, Jay Leno, Garry Shandling, Martin Short and Sandra Bernhard to reveal what makes them tick. The interviews feature in his new book, Sick In The Head: Conversations About Life and Comedy.

"It wasn't about fear – I was just obsessed with getting in a room with these people. I loved them on television, but I wanted to connect with them, I wanted to be able to have a relationship with them."

He started stand-up at 17 but didn't really shine. "I was way too young to be doing stand-up," he says. "I didn't have a lot of strong opinions. I didn't know myself very well and I wasn't very angry. I didn't have any great stories."

At 24, he began writing for other people, and found he was good at it. "I just took it as a sign of the universe telling me that that's where I should put my energy." From there, he took up directing because he was worried people would ruin his work. "When you're a writer, you slowly realise that if you don't want your work to get screwed up, you better start directing some of it."

His new film, Trainwreck, marks a turning point – it is the first of his films he didn't write. Penned by and starring the world's current comedic obsession, Amy Schumer, as a magazine writer with a pathological fear of commitment, its humour spins on a litany of awkward one-night stands but its heart comes from real life.

Apatow asked Schumer to make a movie with him after he heard her talk about her dad's multiple sclerosis on The Howard Stern Show in the US. "She's just so, so smart. I'd seen her do stand-up, but back then her act consisted of a lot of great short jokes," he remembers. "On Howard Stern she was telling elaborate stories about her father and her relationships, and I thought, 'Oh, these are movies'.  I just had this instinct that she was a really great storyteller, and I'd never had that before."

Indeed, Apatow's strength (aside from writing and directing) seems to be in shepherding the careers of burgeoning comedy superstars. (He describes himself as a "helpful leech".)  In addition to Schumer, he's championed the careers of Seth Rogen, ​Jonah Hill, Melissa McCarthy, Lena Dunham​ and Steve Carrell, relishing ongoing collaborations with people he's mentored.

Inspiration can also be found at home, working with wife Mann (the pair met on the set of The Cable Guy in 1996 and married the following year), as well as daughters Maude and Iris (both of whom appeared in Knocked Up and This Is 40). "It's fun to sit with the people you care about more than anyone in the world and try to find ways to express ideas," he says. "We just have a blast doing it. I'm excited to think of more things to do together."

Success doesn't come without attention – good and bad - and the big knock on Apatow has been that his movies have been unashamedly skewed towards the male point of view, with occasionally questionable representation of women (harsher critics suggested his films verged on sexist and misogynistic). It's a charge that annoys him greatly.

"The first big job I had was writing jokes for [unapologetic feminist] Roseanne Barr in 1989," he says, firmly. "I never looked at [my work] in terms of male or female; I always thought about it in terms of who's funny and who had something interesting to say."

There's no denying that his work has changed, though. "I think what's changed is, I have found brilliant women to collaborate with, so in working with Lena [Dunham] and Kristen [Wiig] and Amy [Mumolo] and Amy [Schumer], I've just been lucky enough to go on these creative rides with these people who have a very strong point of view, and it's been ridiculously fun."

He hopes the emergence of Dunham, Schumer, Wiig and McCarthy will inspire other young women to become directors, writers, actors and producers. "We need these people in our industry," he says. "It's certainly been way too male-dominated for too long."

Indeed, Apatow points to the wildly successful Bridesmaids (which he produced), and the fact that it didn't, as expected, start a tsunami of female-dominated movies in Hollywood after its release.

"I think it's much harder to write a good movie for women than for men, because men are just generally happy to just blow some crap up," he says. "Women are more sophisticated and would like movies with complex emotions and stories, and those are just harder to make."

He does think the criticisms levelled at Schumer and Dunham – particularly in their frankness about sex – reeks of a shocking double standard.

"I'm not sure why people get threatened by them, because I've always enjoyed the way they both talk about sex," he says with a laugh. "I would assume it might reveal more about men being threatened by their own sexual issues when they can't handle it. Some men are not conditioned to hearing such frank discussion from the female point of view, but I think it's really healthy and we need more of it. Things are changing in the best possible way."

Apatow admits his own career took a successful turn once he started writing honestly about his personal experiences. "For a long time, I just thought that my life wasn't that interesting, and my opinions weren't that interesting, and when I dropped that, I found that everything that I've done since, people have connected with more.

"When we were making Trainwreck, there's a funny scene where Amy doesn't like to cuddle after sex. It keeps her up all night, because she doesn't want anyone touching her. And Amy and I were laughing about that in the writing process, how we all have these post-sex sleep issues. It's one of the funniest scenes in the movie, and I think it's because when you admit something that's true, millions of people go, 'Oh, yeah, that's the same for me'. Everyone can relate to weird sex issues. I've just made a career out of it."

Trainwreck opens in cinemas on July 30.