"When I was your age I was before the mast on a square rigged ship that ran to Africa"

"Before the mast" means to serve "as a common sailor, because the sailors live in the forecastle, forward of the foremast."

According to Wikipedia, "Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or square, to the keel of the vessel and to the masts." Below is a video of the lovely French square-rigged ship Belem sailing into Boston Harbor in 2008.