Complex sentence: Johannes became head of the family in 1650 when he was 25 years old, although the States-General of the Netherlands decided in the same year he was allowed to keep his title and call himself "patroon" of Rensselaerswijck, but without any legal power.
Split into simpler sentences: Johannes became head of the family in 1650 when he was 25 years old. The States-General of the Netherlands decided in the same year he was allowed to keep his title and call himself "patron" of Rensselaerswyck, but without any legal power.