Good question. Short answer: they’re really old.
We know that bur oaks are one of the slowest growing and longest-lived native North American oaks, case and that they can live hundreds of years. The largest of the oaks in our neighbourhood are more than a metre across the trunk, so we also know that they are between 130 and 180 years old. Long before Sir John A. MacDonald! One tree (preserved at the Champlain Park Field house) has been definitely dated by a specialist as having turned from acorn to sapling in 1856.