Complex sentence: He studied drawing and geometry, and at the age of twenty three qualified for the title of engineer, and entered the service of the Duc de Chevreuse and the Duc de Luynes at the Château de Dampierre, where he taught drawing and mathematics to the children.
Split into simpler sentences: He studied drawing and geometry, and at the age of twenty three qualified for the title of engineer. At the age of twenty-three he qualified for the title of engineer, and entered the service of the Duc de Chevreuse and the Duc de Luynes at the Château de Dampierre, where he taught drawing and mathematics to the children.