I love this movie tooo and watched it many times! I love ALL the songs and I have sung them in school plays, in shower, everywhere! The songs are so addictive and nice to learn and teach the young.
And this is an interesting question:

Does drones already exists in 1960's? because the scenery view shown at the start of the movie was like drone assisted or how did they filmed it?

Haha.. Now you have made me wonder too. I think they probably flew an actual plane back then, to film that scene.

Guess what, I did a search and found this:
https://www.dailymail.co.uk/news/article-3000935/How-did-film-Sound-Music-opening-scene-age-computer-graphics-drones-Julie-Andrews-recalls-making-legendary-movie-50th-anniversary.html
"Julie Andrews has revealed how the spectacular hilltop opening scene of the Sound of Music took a week to shoot because it was filmed with a helicopter before filmmakers had drones at their disposal.

The famous scene sees the actress throw herself into a full-bodied twirl with her arms outstretched and sing the film’s opening words: ‘The hills are alive...’"