Complex sentence: He lived with his parents working on their farm until April 1855 when he moved to Montreal and became the first partner (at age 23) of his elder brother Alexander (age 26) with A. W. Ogilvie & Co., millers and grain dealers.
Split into simpler sentences: He lived with his parents working on their farm until April 1855 when he moved to Montreal. In Montreal, he became the first partner (at age 23) of his elder brother Alexander (age 26) with A. W. Ogilvie & Co., millers and grain dealers.