I scarfed LoTR down at 15 -- all three books -- in less than a month. I ripped through all 12 of E.R. Burroughs Mars novels in about a semester when I was 17. I recently picked up LoTR and one of the Mars novels at a bookstore and found that, at the ripe old age of 40, I simply could not read what I've taken to referring to as "stultifyingly thick" prose.
I would have to call ERB mostly a writer for young adolescents.
But you might download "The Mucker" and see what you think. I'd be interested to hear if you think it's any better than the Barsoom books.
When I was 14, I read "BRAVE NEW WORLD", went mad for Huxley and rapidly read EVERYTHING he had ever written. When the N.Y. Times did the big saint Hillary Sunday Magazine article, I was angry to see that BNW was her favorite book; or so she said. I reread the book and wondered why I had ever liked it, as I now found it boring and badly written.
I found E.R. Burroughs at 10 and adored the Tarzan series. Read ALL of them back then. I wonder if I would not like those books, should I reread them now.