Complex sentence: It is not known when or why he added seven years to his stated age, i.e., for a ship's manifest during 1903, he listed his age as 56, and occupation "Lecturer" when he did a lecture tour to Vancouver and San Francisco.
Split into simpler sentences: It is not known when or why he added seven years to his stated age. For a ship's manifest during 1903, he listed his age as 56, and occupation "Lecturer" when he did a lecture tour to Vancouver and San Francisco.