The girl who played Maya..

And? She looked the part.

Also Troian was the oldest of the Liars and she was playing a teenager.

Bianca Lawson looked very young then and still looks young now. She was able to play the part and kudos to her.

Peace, Love, and Soul 

She played the part well, but I disagree that she looked young enough to play a teenager. She definitely didn't look her actual age, which I believe was 32 or 33 at the time, but looked about mid-twenties.

Coming from a producer/casting director who is often casting for my or my friends projects, age literally means nothing. Sometimes someone can be in their late 30's and look like they're 18. It all depends on what the director is looking for and more often than not someone older can definitely play someone younger. We have never asked an actor/actress their are because if they look a certain age their actual age doesn't matter at all.