Do young singers need to rotate their roles but not older ones?

Question

This question is based on the following line in the Wikipedia article on Éponine (a character from Les Miserables):

Éponine is also featured in the stage musical adaptation. She is played by two actors, a young girl for Young Éponine in the Montfermeil scenes, and by a young woman for the adolescent Éponine in the later Parisian scenes. Actresses playing Young Éponine and Young Cosette sometimes interchange roles in different performances to equalize performance opportunities and vocal strain.

(emphasis mine)

Is this something only young actresses do, and not older ones? If so, why - is there a biological explanation, or something else? The sentence is not cited, so it could also be wrong, in which case that would also be an answer.

Answer 1

This sounds unlikely. The young Cosette is a relatively demanding singing role for a child. The young Eponine is a silent role, so presumably far easier to cast. Since there are usually strict limits on how often children are allowed to perform, it would be illogical to 'waste' a valuable Cosette and have her play Eponine. But maybe they do it anyway to give their Cosettes a break from singing.

For a different show with two similar child roles (e.g. 'The Sound of Music'), companies will often train children for both parts so they are more flexible in their planning.