Athena tells Telemachus,"You must not cling to your boyhood any longer - it's time you were a man." What two things is she advising him to do?

She is telling him to mature and act more manly

One thing she is advising him to do is grow up, as you can see when she says " ... it's time you were a man." Another thing she is advising him is that he needs to learn independence, example being "You must not cling to your boyhood any longer ... ", meaning he is afraid to let go of childhood, and therefore his safety.