Kabbalistic tradition teaches us that Adam, the first human being, was also the first person to study Kabbalah, as well as compiling the book "Raziel the Angel". The book is a compendium of the Kabbalistic secrets Adam learnt after he was banished from the Garden of Eden.
The tradition teaches that in every generation there were special individuals who studied Kabbalah and its secrets, including Hanoch, Noah, Abraham and other righteous people.
However, though with us since the dawn of creation, it was forbidden to reveal the Kabbalah's very existence to the masses. Even the 'Zohar', written in the second century, C.E., was hidden, remaining totally unknown until being rediscovered by the Spanish Kabbalist, Rabbi Moshe De Leon at the end of the 13th century.
Because of the restrictions on the study of Kabbala, only very selected individuals were allowed to delve into its mysteries. This was defined as being a married man above the age of 40 who had already mastered all aspects of the Oral Torah, and who was capable of intellectual understanding of abstract spiritual concepts, was of 'high soul' and more. If such a person could be found, he was allowed to ask a Kabbalah teacher to take him into the world of mystical wisdom and secrets, and even then, acceptance was not guaranteed.
The prohibition regarding learning and spreading Kabbalah in the past was based on our sages' real fear that lofty and highly spiritual Kabbalistic concepts would be misunderstood and misinterpreted, leading to dire consequences, like the anthropomorphism of G-d, distortion of ideas and even crises of faith.