At the end of the day, actors are actors and if they can make what they say and do believable then it's good enough in my opinion. If you can make an old lady look like a young girl and have her play that role in a TV show or movie I'd go along with that because it shows how well her acting skills are and how creative she can be. My whole thing is that, if the actor can pull off the character they're playing, let them have at it.
The age of the character can be vastly different than the actor's actual age. The actor is often cast in a production because of their look which can be different than what they are in real life. The age of the actor doesn't matter, it is the skill of the actor that makes a character authenic.
I dont think someone's matters if they are effectively able to portray the character they are supposed to. The audience does not care about what the actor's actual age is as long as they can convince the audience of the character they are portraying. It matters more on the actors performance than the actual age
What makes television, movies and entertainment possible is the audience member's ability to suspend disbelief. Most people in the 1990s knew that the Olson twins were two people who played the role of one child character on a television program called "Full House." The notion that Hollywood needs to conform to reality in any way is misguided and illogical.
If anyone has seen Hanna Montana, the kid with the moptop was actually in his 30s, but was playing around her age. There was a creepy movie from the 80s where a 30 year old man actually played a 12 year old looking kid...And pulled it off. Looks and age don't always correspond. If they can act the part, go for it.