How to become sophisticated?

J., a nascent MR reader, requests:

Which journals, magazines and blogs should a 15yo read in order to be considered a widely sophisticated and educated person 20 years later (not necessarily to show off or to impress others but for one's own good feeling)?

I do not have a concrete answer.  When I was 12-13, I was very interested in chess and not so interested in culturally sophisticated outputs, unless you count the Beatles and jazz guitar and baseball.  I am glad that I spent most of my time then reading in those areas because I cared about them deeply at the time.  Those investments will then help us learn other areas, so it is learning about how to learn.  At age 21 it was all about German Romanticism for me, and at 22 analytic philosophy.  Find grooves, and push on them until your ardor abates.  Until the very end, there is always time to learn more areas, and always a very large number of areas one does not know at all.

It has become a cliche, but Samuel Johnson was close to the truth when he wrote:

"A man should read as his fancy takes him, for what he reads as a chore will do him little good."

I don't recommend that attitude for mastering technical subjects, but for general sophistication it is right on.  The most sophisticated person is someone who really loves an area and has pursued it, and that's also the best magnet for attracting interested and interesting others.  On related topics, here is Modeled Behavior and here is Robin Hanson.