Do you happen to know where in the letters this appears?
I haven't found the letter you're talking about yet. I checked the few index references to Merry and Pippin and found that C.S. Lewis didn't like hobbits and Merry and Pippin least of all!
The nerve of some people! :)
I feel like going off on a Lewis (allegory-boy) bash this morning! Otherwise, I'm checking the Frodo and Sam references today.
Do you happen to know where in the letters this appears?
I have found something close in Letter 177 (to Rayner Unwin dated 8 Dec. 1955.) "Edwin Muir, reviewing The Return of the King in the Observer on 27 November, wrote:'All the characters are boys masquerading as adult heroes....and will never come to puberty.....Hardly one of them knows anything about women.'"
To which Tolkien replied:
Blast Edwin Muir and his delayed adolescence. He is old enough to know better. It might do him good to hear what women think of his 'knowing about women', especially as a test of being mentally adult. If he had an M.A. I should nominate him for the professorship of poetry-a sweet revenge.[A footnote about the poetry professorship [at Oxford] states that it was vacant at the time and nominations were being made for his successor. W.H. Auden was elected. He's the guy who said "If someone dislikes it [LOTR], I shall never trust their literary judgement about anything again."]
I'm not sure why that would be a sweet revenge (but then, sometimes I'm a slowcoach!)