He may be referring to a passage by the businessman Callicles in Plato's Gorgias.
Philosophy, as a part of education, is an excellent thing, and there
is no disgrace to a man while he is young in pursuing such a study;
but when he is more advanced in years, the thing becomes ridiculous,
and I feel towards philosophers as I do towards those who lisp and
imitate children. For I love to see a little child, who is not of an
age to speak plainly, lisping at his play; there is an appearance of
grace and freedom in his utterance, which is natural to his childish
years. But when I hear some small creature carefully articulating its
words, I am offended; the sound is disagreeable, and has to my ears
the twang of slavery. So when I hear a man lisping, or see him playing
like a child, his behaviour appears to me ridiculous and unmanly and
worthy of stripes. And I have the same feeling about students of
philosophy; when I see a youth thus engaged,—the study appears to me
to be in character, and becoming a man of liberal education, and him
who neglects philosophy I regard as an inferior man, who will never
aspire to anything great or noble. But if I see him continuing the
study in later life, and not leaving off, I should like to beat him,
Socrates; for, as I was saying, such a one, even though he have good
natural parts, becomes effeminate. He flies from the busy centre and
the market-place, in which, as the poet says, men become
distinguished; he creeps into a corner for the rest of his life, and
talks in a whisper with three or four admiring youths, but never
speaks out like a freeman in a satisfactory manner.