Even today the definitions differ: members of one generation may see masculinity in the strong jawline of actor George Clooney, and others may see it in the nonthreatening coif of pop star Justin Bieber.
Personally, I like this quotation from Norman Mailer:
Masculinity is not something given to you, but something you gain. And you gain it by winning small battles with honor.Whether those battles involve defeating the Cyclops or rising through the pop charts is up to you.
(Photo of George Clooney from Wikipedia.)