Hello, I would like to know the exactly meaning of this OUT in this GROW OUT:
' Glenn was seventeen years old when he GREW naturally into a simpathy "with the flamboyant extroversion of the young Richard Strauss ... - Glenn says - (and) I have never GROWN OUT of it."
It does mean that he never left growing into its admiration for R.Strauss? ... that never ceased his admiration for R.Strauss?

Thanks in advance, jo.
It means that, as he grew older, his admiration for R. S. never stopped.
Yes; it's a fossilised metaphor: as children, we "grow out of" our clothes, when they become too small for us.

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Glenn felt that there was something immature about being sympathetic with the flamboyant extroversion in question. He felt that as he matured he would (possibly should) become less sympathetic with it. We "grow out of" our immature, childish ways when we mature and become adults. But in some cases, we never give up some of our earlier habits or ways of thinking, even as adults. In those cases we say that we never "grew out of" those immature habits or ways of thinking. A very extreme case might be: "John always sucked his thumb as a child. He is now 42 years old, and he has never grown out of it!" Emotion: smile (That is, he still sucks his thumb!)

(I'm not sure I saw the 'admiration' angle of this.)

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