When you're playing a teen on screen, it helps if you're short. It generally means you can carry on playing the part long after your teenage years are behind you, because you still have the (lack of) height to pull it off. That's how Frankie Muniz managed to carry on playing 'Malcolm in the Middle' for as long as he did - he's 5 foot 5. He could probably have done even more as an actor in his younger years, but he never treated it as a priority. He tried to break into motor racing for a while, and also drummed for an indie rock band.
Sadly, Muniz suffered a stroke a few years ago, and it had a debilitating effect on his career. He's recovering well, but said in 2017 that the stroke had robbed him of many of his memories, including most of his time in 'Malcolm in the Middle.' He also doesn't take on much acting work anymore, because he struggles to remember lines. He can still light up a screen though, which is why he makes such a natural host of 'Dancing with The Stars: Juniors.'