If directors want to cast octogenarians in roles meant for actors fifty years younger, then that's their purview and I look forward to the results. But it's hard to deny that it doesn't alter the authorial intent.
Personally I don't think anyone over 50 should be playing Higgins and better yet someone in their 30's or 40's. (Rex Harrison was 48 for the debut and 56 for the film. He was 73, I think, for the revival and the consensus was that he was too old.)