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The Greek adverb anothen (ἄνωθεν) means double meaning: "anew, again" or "from above." In other words, the issue is whether one is born from above or born again. The NRSV and some other translations render the adverb as the former. The NIV takes it as the latter.
Jesus does not seem to mean "again" because it is Nicodemus who mistook it as he asks: “How can anyone be born after having grown old? Can one enter a second time into the mother’s womb and be born?” (John 3:4).
Then, Jesus answers him: "Very truly, I tell you, no one can enter the kingdom of God without being born of water and Spirit" (John 3:5). He unpacks the meaning of "from above." Such a person born from above must have water baptism in which one receives the Spirit. More directly, "born of the Spirit" corresponds to "born from above" in 3:3. The Spirit comes from above, God. It is God's Spirit. Therefore, "born from above" implies that one has to depend on God or the Spirit to live a new life. Likewise, one needs to be constantly informed and molded by the Spirit. Spiritual birth comes from the Spirit and does not have a birthdate. It can maintain itself through ongoing spiritual renewal.
*The book regarding the above: Truth, Testimony, and Transformation.