Fourteen.
I don’t think most people would disagree that “teenager” is a more accurate word to describe that age. Trust me, there is plenty fucked up with the OP picture, we don’t need to resort to hyperbolic language to get our point across.
Its not hyperbolic, 14 is a teenage child. Teenager is not more accurate, because when you say a ‘teenage worker’ most would assume they were at least in the usually accepted ‘young adult’ range, 16-19, the image here is of a child worker. If they were 17 or 16 that might be different, though still literally, legally a child.