Lucy Cowdery Young, Oliver's half-sister, gives short biography of Oliver Cowdery; mentions he left for NY in circa 1825 and met the Smiths circa 1829.
Lucy C. Young, Letter to "Brigham," March 7, 1887, CHL, MS 842
Now in regard to Oliver he was born in the town of Wells in the State of Vermont when he was three years of age Father married my mother she resided in the town of Pullney <Poultney> so Oliver was brought up in Poultney Rutland County Vermont, and when he arrived at the age of twenty he went to the State of New York where his older brothers were married there his Olivers occupation was clerking in a store until 1829 when he taught the District school in the town of Manchester nine miles from Fathers . . . he was born one Thousand Eight hundred and give in the month of October I think but I cannot remember the day of the month