Gender - what does it really mean?

I've wondered a lot over the years what we really mean by masculinity and femininity, what makes a woman womanly or a man manly.

What is tripping me up is that there's no quality I can think of, that a real man ought to aspire to, that a woman ought not to have as well; and vice versa.

And when I think of characteristics that we associate with boys and men, or girls and women, there aren't any that aren't a trainwreck if taken to the extreme. Men who are too aggressive. Women who are too invested in their appearance. Women who smother their children so they have to make a complete break to get away. Men who have to dominate everyone around them.

Here is Rudyard Kipling's "If". It goes through a lot of "if you can" this and that, and ends
"Yours is the Earth and everything that’s in it,
And — which is more — you’ll be a Man, my son!"

Does he really mean "man", or does he mean "grownup"?

Look at this part:

"If you can bear to ...
... watch the things you gave your life to, broken,
And stoop and build ’em up with worn-out tools"

Think about a mother who did the best she could to raise her child but in his teen years he fell in with the wrong crowd. Drugs. Problems in school. Maybe he develops an addiction, or actually ends up in prison. The mom addresses his problems at the same time that she loves him unconditionally, which is to say no matter what, and never gives up on him. Is that not womanly?

This part:

"If you can make one heap of all your winnings
And risk it on one turn of pitch-and-toss,
And lose, and start again at your beginnings
And never breathe a word about your loss;"

That's cool, but if you are gambling away the rent money or any money beyond your discretionary spending, you may or may not be a man, but you're definitely a fool.

So anyway, suppose you take a quality like nurturing. Maybe women tend more to have this quality than men. That doesn't mean that any given woman is nurturing. That doesn't mean that men aren't. When I am sick my husband takes very good care of me. I don't see that as womanish. I see that as my life partner caring and stepping up. Why would I want a partner who didn't.

When I've tried asking this before I've never gotten a straight answer. I have read where feminists (dunh dunh DUNH!) assert that there is no difference between men and women. I don't see other feminists saying this and I don't say it either. I know we're different. Of course we are. I'm just not sure exactly how.

Thoughts?