James Calhoun was the brother-in-law of a soldier who was brevetted to brigadier general at what age?
James Calhoun (soldier):  He was the brother-in-law of George Armstrong Custer and was killed along with Custer in the Battle of the Little Bighorn. George Armstrong Custer:  Custer was brevetted to brigadier general at age 23, less than a week before the Battle of Gettysburg, where he personally led cavalry charges that prevented Confederate cavalry from attacking the Union rear in support of Pickett's Charge.
23