Complex sentence: Initially studying at the local college of the St. Mary's church, he was sent to Gniew to study Polish language at the age of 13 before returning to Danzig to study at the Academic Gymnasium, the distant predecessor of the modern University of Gdańsk.
Split into simpler sentences: Initially studying at the local college of the St. Mary's church, at the age of 13 he was dispatched to Gniew to study Polish language. Then he studied at the Danzig-based Academic Gymnasium, the distant predecessor of the modern University of Gdańsk.