it was 3 years ago when I saw the movie for the first time. (emphasize on 3 years ago) The first time I saw the movie was 3 years ago.(emphasize on the first time) The first time I saw the movie I was 13.

I first saw this movie 3 years ago I first saw this movie when I was 13

Yes! On a style point, write the numerals as words (three... thirteen).

The sentences are grammatically correct. But usually we say: It was three years ago when I first saw the movie. (The first sentence) The second sentence looks right to me. :-)