Christopher Plummer: "If I slow down now, I'll die"

It won best picture and is still one of the most beloved movies of all time. With its stunning scenery, charming story and memorable songs, "The Sound of Music" has warmed the hearts of viewers for years.

But its star Christopher Plummer hasn't always been as fond of the 1965 big-screen musical, which is celebrating its 50-year anniversary this month.

Plummer played Captain Georg von Trapp, a retired Austrian naval officer raising his seven children alone using a military-style discipline following the death of his wife. That's until Maria (Julie Andrews) comes along. After leaving an Austrian convent to become the kids' governess, she reintroduces music to the family, which softens up an otherwise hardened man.

Thanks to the songs "Edelweiss," "My Favorite Things," "Climb Ev'ry Mountain" and "Do-Re-Mi," the movie has held a firm place in history -- and continues to live on with annual television airings, sing-a-long events and more.

Lady Gaga recently brought the musical's songs to life with her Feb. 22 Oscars performance, which received rave reviews and became the Academy Awards' top social moment. It even got a big thumbs up from Andrews, who greeted the singer onstage, saying, "Dear Lady Gaga, thank you for that wonderful tribute. It really warmed my heart."

But if you ask Plummer, he's tired of talking a film that debuted a half-century ago.

"One doesn't go on and on talking about other movies forever and ever," he said. "You make them, you love doing them. You even may respect them, but you forget about them because life goes on and you've got other things to do. And every so often this thing raises its head...I'm so sick of hearing my own voice talking about it."

Still, he graciously took some time out to speak to CBS News about it. During the chat, Plummer said he doesn't hate the movie -- he never did.

"I just didn't particularly think my role was the most exciting thing I've ever had in my life," he said.

"I had been spoiled -- I already played Hamlet and all those great parts in the theater in England and Canada and New York. And then suddenly to be faced with Captain Von Trapp, it didn't sort of hold a candle somehow," he continued laughing. "But I thought I would be a good boy and take my medicine. And besides 'I'd like to be in musical...It would give me an idea of what it's like to be in one.' So, for all those reasons I went ahead."

Plummer admits that he was sort of the "bad boy" on-set -- and looking back, he thinks that was a positive thing.

"It was good to see someone who was irreverent on the set. There were so many nuns around it was frightening. I didn't know who to be more afraid of -- the Nazis or the nuns!" Plummer said with a chuckle.

In all seriousness, Plummer said he has many fond memories from that time and that there were many "pluses" to the film.

The kids were sweet, he says. And so was Eleanor Parker, the actress who played Elsa von Schraeder, Captain Von Trapp's love interest from Vienna.

"I had a great crush on her," revealed Plummer.

He called director Robert Wise "a tremendously skilled director and real gentleman -- a rare thing in our business."

And then there was the beautiful countryside.

"How could you go wrong?" said Plummer about the film, which shot on location in Salzburg, Austria.

One drawback? Plummer put on a lot of weight, so much so that they had to adjust his wardrobe.

"When I came back from our days off in Vienna -- where I had a ball -- Robert Wise, said, 'You look like Orson Welles. We gotta redo your costume.'"

Another plus? Julie Andrews, of course.

"I love Julie," said Plummer. "I thought she was absolutely smashing in it. I think it's the best thing she's ever done. She's at her most natural...She stripped all of her layers away and made herself vulnerable and real. And it's hard to be vulnerable and real -- and be a singer, too...I was absolutely filled with admiration for her."

Plummer, 85, and Andrews, 79, have stayed in touch over the years, appearing in the 2001 CBS TV film, "On Golden Pond," for example. They're expected to reunite later this month for a special anniversary event, too.

Plummer, meanwhile, remembers the exact moment when he finally came to peace with the film. It happened in 2008 when he was forced to watch it "at some children's party which I couldn't get out of."

He hadn't seen it ages and was pleasantly surprised.

"I was filled with admiration about how they managed to make it not too sentimental...And so I was very impressed with it," said Plummer.

But don't expect Plummer to sit down for another viewing.

"I didn't need to see it again. And I was so nice about it that I thought, 'I better not see it again in case I change my mind!" he said with a laugh.

So, if it's not "The Sound of Music," then what are Plummer's favorite roles of all time?

The actor, who got his start in the theater, says several parts stand out in his mind.

"I was so spoiled with parts I was given to play, so I should be very happy about everything. 'Henry V' is what catapulted me in my career. That was a lovely production. I think that found my feet in that as a classical actor...I've done every classical role there is...I mean how rich can you get?"

On the big screen, Plummer has a few favorites, too -- though he says he'd much rather go see other people's movies.

"I really did like playing Mike Wallace in ['The Insider']. That was a good film," Plummer said about the 1999 movie, co-starring Al Pacino and Russell Crowe. "And I loved John Huston's 'The Man Who Would Be King.'"

Plummer also loved "Beginners," the 2012 movie that earned him his first-ever Oscar at the age of 82. In it, Plummer portrays Hal Fields, who after a long marriage announces he's gay and takes up with a young lover. His best-supporting-acting win made him oldest person to receive an Oscar in the history of the Academy Awards.

He knew it was a great part, but says he never imagined he'd win an Oscar for it.

"Not only was it well-written and it was funny and touching, but it offered me an enormous range and it offered me a freedom to do what I wanted with it. So I felt completely natural in it. I believed it, which you don't always do with every part you play," Plummer reflected. "And I was very comfortable in that film. That's as far as it went...I didn't think, 'Oh hey, this is going to get an Oscar.' You don't think like that."

Looking ahead, Plummer has several new roles coming up, including a part alongside John Travolta in "The Forger" and an upcoming role in "Danny Collins" with Al Pacino.

"This part was great fun because he's [Pacino] an old rock star who's trying to get his feet again. And I'm his crusty old manager...It's beautifully written by Dan Fogelman," said Plummer.

Also coming up is the new thriller "Remember" and a voice role in animated film "Red and Grays."

"I'm trying to play these roles of a certain age, but they are all different. And I am very determined to make them all different, so I don't look like the same old man playing the same old man. Sometimes I have to wear a hat to do something really outrageous," Plummer joked.

Plummer says the work keeps him young, which means he doesn't expect to slow down any time soon.

"Retirement is just not possible...If I slow down now, I'll die. I'll drop dead," he said.