Why would Jessie Mueller be too young? She's 35. Jan Clayton was 27 when she created the role, and Iva Withers, who played far more performances as Julie than Clayton (or anyone else) played, was 28 when she took over from Clayton.
It's impossible for me to fathom Mueller as too young, or too old (which I read elsewhere, startlingly enough). The actor must portray two very different eras of this woman's life persuasively, the only overall requirement.
