Reddit mentions of Aesthetics and Politics (Radical Thinkers)

You've hit the nail on the head here. It's not a matter of age so much as a learned or accumulated ability to critically appraise books. I was the same in that I would generally read books and say 'it was great' or 'it was bad' without necessarily being able to explain why. But with practice, effort and a little research you can develop that critical insight. Try reading reviews of the books you have read - do you agree with the points raised? Do you think the reviewer is missing the point? Write down your own thoughts about the book.

There are also some great resources for developing critical thinking in general, and a critical understanding of literature. Check out this video of a Yale lecture about Literary Criticism ... or if that's a bit heavy, try:

• John Green's Crash Course on English Literature
  
• Draw My Literary Theory
  
• Thug Notes
  
  EDIT: and here are some interesting books that I've read about literature, criticism, and so on...
  
  
• Patricia Waugh - Modern Literary Theory: an Oxford Guide - a very big book that you can dip into for interesting articles, just use as a reference book if you want to look something up, or read cover to cover. It's a large collection of essays on different aspects of literary theory
  
• Adorno et al - Aesthetics and Politics - a collection of essays by Theodor Adorno, Walter Benjamin, Ernst Bloch, Bertolt Brecht & Georg Lukacs presented as a series of discussions between the different theorists (pointing out where Bloch's essay is responding to Lukacs' essay or what have you)
  
• Walter Benjamin - Illuminations - Benjamin was one of the most influential critics of the 20th century, and his essay The Work of Art in the Age of Mechanical Reproduction is on a lot of university reading lists for all kinds of subjects.

For a Marxist/ Critical Theory perspective, I found this collection to be interesting: https://www.amazon.com/Aesthetics-Politics-Radical-Thinkers-Theodor/dp/184467570X

This isn't exactly what you asked for, but a lot of it involves expressionism: http://www.amazon.com/Aesthetics-Politics-Radical-Thinkers-Theodor/dp/184467570X/ref=sr_1_1?ie=UTF8&qid=1463536280&sr=8-1&keywords=aesthetics+and+politics

Can I throw a recommendation your way? If you're liking Artaud and Debord you might be interested in some of their German contemporaries who were working in theater and aesthetic/political theory- there's a cool collection called Aesthetics and Politics that includes key passages from Adorno, Benjamin, Brecht, and a couple others that I dipped into a few years ago and loved. You'd probably be interested in the play Ubu Roi too!