The idea that the 33 years of Jesus' life correspond to the 33 vertebrae in the human spine is not based on any historical or religious evidence. Instead, it seems to have emerged in various esoteric and mystical traditions in the late 19th and early 20th centuries. Here are some sources that provide more information about the origins and development of this teaching:
"Theosophy and the Spine" by Joy Mills (Theosophical Society in America) - This article explores the Theosophical Society's beliefs about the spiritual significance of the spine and its relationship to consciousness and spiritual awakening.
"The Spiritual Significance of the Human Spine" by Jason Gregory (New Dawn Magazine) - This article discusses the spiritual and philosophical views of René Guénon and other esoteric thinkers on the spine and its role in spiritual development.
"The Esoteric Meaning of the 33 Vertebrae" by Robert Guffey (Mysterious Universe) - This article provides a brief overview of the idea that the 33 years of Jesus' life correspond to the 33 vertebrae in the human spine, and discusses some of the possible origins of this belief.
"Theosophical Society" (Encyclopedia Britannica) - This entry provides a brief history and overview of the Theosophical Society, including its beliefs about the spiritual significance of the spine.
"René Guénon and the Spiritual Science of the Spine" by Joscelyn Godwin (New Dawn Magazine) - This article discusses the esoteric teachings of René Guénon and his views on the spine and its role in spiritual awakening.
It's worth noting that these sources are all from esoteric and mystical traditions, and do not represent mainstream Christian theology or scholarship. As such, they should be regarded as speculative and subjective interpretations of religious and spiritual ideas.