Complex sentence: Dugdale became a Catholic convert, in 1657 or 1658 (being at that date about eighteen years of age), and then met Francis Evers, a Jesuit, in Staffordshire.
Split into simpler sentences: Dugdale became a Catholic convert, in 1657 or 1658 (being at that date about eighteen years of age). About the same time he met Francis Evers, a Jesuit, in Staffordshire.