"Murray has years of experience in family practice, but he is just a fledgling in surgery."
In the above sentence, is fledgling a noun or an adjective? Or, is it both? Is that why both noun and adjective definitions are present in the following Magoosh practice link?
Please provide references for your answer, if possible.
P.s. My punctuation needs work. If you notice any punctuation or grammar problems in my question, please say so!