About learning

Today I am going to talk about learning. As food is to the body, so is learning to the mind. If one <strike>who </strike>wants to lead a healthy and meaningful life, he should often find time to lean more knowledge.
But it is a common fallacy to regard school as the only place to gain knowledge. On the contrary, learning should be a never-ending process, from the cradle to the grave. In my opinion, graduation from <strike>the </strike>school is not the end of <em>one's studies.</em> Just as an old saying goes, it is never too late to learn. People have to take learning as a lifelong career.
What’s worse, more and more people believe that learning new skills and knowledge is just for getting more job opportunities or get promotions. They think the aim of learning is just earning more money. However, I think the key to success is not earning much money, but getting more knowledge and improving ourselves mentally. We should improve our ways of thinking and enjoy the joy of exchanging excellent ideas by learning.
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The corrections above are just how I think it should be.

Your English is excellent indeed. I agree with your thoughts on learning too.

You should use plural all the way through. Elephants have long noses. Cats have sharp claws. People have faces. Do you see what I mean?

Is your house yours? If yes, then why can't you order it to keep rat infestations out? Why won't it listen to you? Because it can't. Same thing with bodies, really. It can't just keep away from a viral or bacterial illness because you want it to.

Spongebob! Dexter's Laboratory. Courage the Cowardly Dog All those are cartoons though, sorry. The only one I know with kids in it is Barney.

Personally, I find it perfectly fine as a first person singular contraction of the conjugation "to be" The real one: Aren't I cool? But you're saying, "Are I not cool?" which doesn't really make sense. I suggest ain't as a better alternative. But nobody ever listens to me. :P

It just means, "Who are you?" but in sort of a forceful or mean way.

"Why cannot I be happy" is not something a native speaker would ever say unless they're especially eccentric. "Why can I not be happy?" works. I hope you can find a way to be happy though, Yagiz. :P