Why not just have a best actor award?
Granted, there are some parts that must have a female actor or a male actor, just as some parts must be played by an old or a young actor. 'Old' in fact indicates an esential distinction, regarding both identity and the parts played.
Maybe we should have Oscars, Baftas, etc awarded for "old actor" or "young actor" or "tall actor","short actor","heavy actor", "skinny actor"...