John 3:4

when he is old He purposely puts the most impossible case; the words do not imply that he was an old man himself. It is difficult to believe that Nicodemus really supposed Christ to be speaking of ordinary birth; the metaphor of -new birth" for spiritual regeneration cannot have been unfamiliar to him. Either he purposely misunderstands, in order to reduce Christ's words to an absurdity; or, more probably, not knowing what to say, he asks what he knew to be a foolish question.

the second time This expression has contributed to the word which probably means -from above," being translated -again." But -to enter a second time into his mother's womb" is simply a periphrasis for -to be born" in the case of an adult. The word which means -from above" is not included in the periphrasis. It is precisely that which perplexes Nicodemus; so he leaves it out.