I checked the John Gardner quotation in the NYT article, "The Problem with Meaning" by David Brooks. I also read the first several of the NYT picks of the comments. These add several important dimensions to the article. Your chosen quote, though, of the things you learn in maturity - is very well stated. I'm not sure if those things you learn in maturity are teachable. Another quote by David Brooks is in one of the comments: "Everyone is born with a mind...but it is only through introspection, observation, connecting the head and the heart, making meaning of experience and finding an organizing purpose that you build a unique individual self."
I speculate that introspection and observation might be teachable to a certain extent. Some people are very resistant to introspecting or have brains that are constructed so as to make it more difficult.
I actually think Brooks is a blowhard and not often correct. That's why I didn't link the article from which I pulled the quote. Given that it wasn't Brooks who came up with it, I didn't find it necessary to give him any credit. He does, however, happen to be correct in that little snippet you pulled. The rest of the OpEd is garbage, IMO.
Some of the commentators share your opinion. I actually didn't read the Brooks article yet. But my question involves what is teachable. Can introspection be taught? Perhaps taught is the wrong word... maybe prodded is better. Prodding people towards introspection might be the best we can do.