"But if the Oracle said that my son should be killed I would neither dispute it nor be the one to do it."
I was curious as to what an African oracle would look like. I’ve read a lot of Greek mythology, and I have a pretty good idea of what that would look like, but every time they mentioned the oracle I had no idea what to imagine, so I looked it up, and the picture I’ve attached is a general idea of what they looked like. 
'She should have been a boy,'
Here is where the reader can see the difference between Enzima and Nwoye in Okonkwo’s eyes. Enzima has a lot of the characteristics Okonkwo wants in a son, and the only problem with her is that she’s a girl. This ties in with Okonkwo’s values, because he only praises masculinity and strength in men. He recognizes it in Enzima, but doesn’t praise her for it because she’s not a man.
Nwoye overheard it and burst into tears, whereupon his father beat him heavily.
Okonkwo’s relationship with his father is obviously present when he’s being brought up in the novel, but also in situations like these where he beats his own son for acting weak. He can’t stand anything other than strength, especially from a man, because of the weakness his own father showed. Okonkwo’s actions toward his children and wives is heavily influenced by his resentment of his father.
Okonkwo ruled his household with a heavy hand. His wives, especially the youngest, lived in perpetual fear of his fiery temper, and so did his little children. Perhaps down in his heart Okonkwo was not a cruel man. But his whole life was dominated by fear, the fear of failure and of weakness. It was deeper and more intimate than the fear of evil and capricious gods and of magic, the fear of the forest, and of the forces of nature, malevolent, red in tooth and claw. Okonkwo's fear was greater than these. It was not external but lay deep within himself. It was the fear of himself, lest he should be found to resemble his father. Even as a little boy he had resented his father's failure and weakness, and even now he still remembered how he had suffered when a playmate had told him that his father was agbala. That was how Okonkwo first came to know that agbala was not only another name for a woman, it could also mean a man who had taken no title. And so Okonkwo was ruled by one passion - to hate everything that his father Unoka had loved. One of those things was gentleness and another was idleness.
Here we perhaps see the origin of Okonkwo's entire perception of masculinity and femininity from his father. The third person narrator brings up that his fear was "...of himself, lest he should be found to resemble his father." He goes overboard in his discipline of his household because he does not want any weakness or mercy to come from him, as this would remind him of his father. This is where his view of masculinity comes into play, in how he expects his sons to behave as he does, so as to not raise anyone like his father.
As for femininity, we see that agbala is another name for a woman at this time, and if he associated his father in that way, then it only makes sense that he would see femininity as an extension of his father. So I believe that his thoughts on masculinity and femininity all originate from his father, as much of adolescence in males can be influenced by father figures, for the better or worse. This article makes some good points on this influence: https://www.psychologytoday.com/blog/the-long-reach-childhood/201106/the-importance-fathers