50 years playing everything Ian McKellen: 'My ambition is to get better as an actor'

• • Emine Saner
  • guardian.co.uk

Ian McKellen in Chichester. Photograph: Helen Maybanks

Next week, it will be 50 years since Sir Ian McKellen first walked out on stage, at the Belgrade theatre in Coventry. "I couldn't believe my luck," he says when I ask him what it felt like. "I had done a lot of theatre-going when I was a kid, which is how I got interested but I had never thought, really, that I would be an actor, it was the sort of thing I would say to adults to stop them asking what I wanted to be when I grew up." Getting a scholarship to Cambridge was what did it, he says. "There were all these people – Derek Jacobi, David Frost, Trevor Nunn – and they were going to go into the theatre. I thought, frankly if they are good enough, I am."

We sit outside on the terrace of the cafe at the smaller Minerva theatre, part of the Chichester festival theatre complex, where McKellen is appearing in Eduardo de Filippo's 1960 play The Syndicate, directed by Sean Mathias, with whom he has worked many times (they also had a long relationship). He demolishes a slice of victoria sponge quicker than I have ever seen anyone do it before, before noticing my chocolate cake. "Are you going to finish that?" he asks. "I've got a waistline to develop." I slide it over to him. How can I say no?

Before I meet McKellen I fear I may love him. He is grand but doesn't take himself seriously, he continues to devote much of his life to campaigning for gay equality, he thinks people who don't live in London should have access to great plays and great actors – just as he did when he was a child, watching John Gielgud on stage in Manchester – which is why he loves going on tour. After Chichester, the company goes to Malvern, then Cambridge, Bath and Milton Keynes. After that, he is back in his wizard robes in New Zealand to film The Hobbit. He had some time off a while ago, thought he might slow down, but didn't really know what to do with himself. Far better to be working.

He plays Don Antonio, a mafia boss who at 75 is haunted by the memory of the person he killed when he was a teenager. "He was whisked off to New York to avoid the courts. He comes back to Naples with all his guns and cunning and ability to organise, and he puts all that at the service of sorting out people's lives in the hope he can stop people killing each other, behaving badly to each other. So he's a Godfather with a twist. I have great faith in it."

Don Antonio emerges in his dressing gown, shadowboxing in a way that is both impressive – he is clearly a man aware of his own power – and sad because the footsteps aren't as light, the punches not as potent. At one point his son says "Seventy-five? You don't look like an old man" – the same can be said for McKellen, three years younger, who today is wearing a fashionable tweed cap and a string of beads around his neck – but mortality is clearly something that weighs on him. Is McKellen aware of getting older? "Oh God," he says with a huge sigh. "If I'm with people of my own age, we talk about it all the time – 'How's your back? So and so's going blind.' You're constantly aware of it. If I have a fall at my age – aaagh!" He throws his hands up. "I did have a fall the other day. I was running for the river bus and it was a bit slippy. I went down, just the day before we started rehearsing. Does that mean I'm going to be in a sling? Have I broken a bone? Things like that. I have got prostate cancer and I have to keep monitoring that. It's no problem, it's under control and I'm very cool about it but other people are dying from it. And the memory – will the time come when I can't remember the lines? So yes, I'm always talking about age."

Is he angry about it? He seems to be. "No!" he almost shouts. "That would be very egotistical, thinking it wasn't appropriate for me to die. But of course, we all think we're immortal a little bit don't we. So working is a way of keeping mortality at bay."

Are there any parts left for McKellen to play? He has been Prospero, Macbeth and Lear. He has done Chekhov, Ibsen and Beckett. And Coronation Street. He has the best wizarding role of all, nominated for his second Oscar for his role as Gandalf in Lord of the Rings. "I would like to do a pantomime again, because I enjoyed that very much," he says when I ask if he has any more ambitions. "We're very lucky, men, that there are these fabulous parts. Women – once you've done all the parts in Shakespeare they start running out. So you can pick and choose and find something to energise you. My ambition is to get better as an actor. I still think there's room for improvement."

I wonder how he copes with the adoration. "Adored?" he says, sounding just surprised enough to make me think he means it. "Am I?" He's a national treasure! He laughs and looks pleased. "It's lovely when someone comes up and says: 'My husband and I saw you in a play, in fact it was our first date,' and I've been a part of their lives without knowing it and they've got a sentimental attachment [to me], as we all do to actors. But I'm only an actor. I'm not a writer. I'm not going to leave any legacy." He pauses. "All I've ever done is learn the lines and say them."

McKellen's campaign work, he says, is "the good stuff. It was the making of me. It gave my life a purpose. I used to comfort myself when I became an actor that it was a useful job, entertaining people. And it was important to do it as well as you possibly can. But being part of the movement that changed the laws in this country that disadvantaged gay people, that's going to affect people in the future."

He came out relatively late – he was 49 – though it was no secret in his immediate circle. And he is still one of very few officially out Hollywood stars. "I think they put up with me because I'm a foreigner. I'm not a danger. It's a bewilderment really – California is full of mavericks and free thinkers. It has the best lesbian and gay youth centres in the world. There are gay police on the streets of west Hollywood and yet the industry itself is nervous, and that's because it's looking over its shoulder at its audience and its audience doesn't come from Hollywood, it comes from the midwest where it's still not easy to be gay. The battle going on over gay marriage in America reveals an awful lot. The Bible belt – people hate gay people. Because the Bible tells them? No, the Bible tells them an awful lot of things that they ignore."

Over the past couple of years, McKellen has visited more than 50 secondary schools on behalf of Stonewall, the campaign group he co-founded. "It's wonderful," he says. "I've met kids who think they're anti-gay and you talk to them and it turns out they don't know much about it, it's not a subject that is talked about. But [to see] a young gay person who, at 14 knows, and comes out successfully to his parents and family, teachers and friends, it's astonishing. When you hear people saying, 'You shouldn't be talking about homosexuality in schools,' well, if you don't there is going to be another generation of people who are confused, bewildered, suspicious, threatened. These kids aren't threatened by it."

They listen because, well, who wouldn't listen to Gandalf? Did he never wish international fame had come to him earlier? Not at all, he says. "If I had become a well-known film actor and thought, now I must have a film career, that's a very difficult thing to organise. Theatre is relatively easy if you're British – you're living in the theatre capital of the world, London, there are so many places you can work, still. If I had begun to think of myself as a film actor I think I would have got distracted. I'm much happier … it has all worked out wonderfully well. I was way into my 60s so my head was not likely to get swollen. I was just glad to be recognised as being an actor who was succeeding. I liked that side of the acclaim, if that's what you call it. To be a star," he almost spits out the word, "that's never appealed to me really."

Later, in the theatre I wait for the play to start. The woman next to me says she came to see it because she always wanted to see Ian McKellen act, adding gravely: "I don't know how long we'll be able to do that for." But when McKellen takes his bow, he looks as if he couldn't feel more at home anywhere else. As far away from retirement as you can imagine.

The Syndicate is on at the Cambridge Arts Theatre from 29 August, then tours to Bath and Milton Keynes in September

• This article was amended on August 25 2011. The original misspelled the name of Eduardo de Filippo. This has been corrected.