Two George Rowan's of about the right age were in Philadelphia in 1850. One was 6 years old, living with Michael and Eliza Rowen; the other was 5, living with Henry and Matilda Rowen. (Both are on 1850 US census, Pennsylvania, Philadelphia, Kensington, ward 5, page 382 verso = 164 handwritten.) I assume one of them is the George Rowan who served in the 91st, but I don't know which.
He was born in 1842/43 (2 (18 in 1861)).
When he enlisted, he was living in Philadelphia, Pennsylvania (2).
He enlisted and was mustered into service, at Philadelphia, Pennsylvania, on 7 October 1861 (1, 2). He was mustered in as a private, in company B (1, 2, 3).
He was not on the muster-out roll when the regiment mustered out (1). He was a private, in company B (3).
1 Bates, Samuel Penniman. History of Pennsylvania volunteers, 1861-5. Harrisburg: B. Singerly, state printer, 1869-71. 5 volumes. 'Ninety-first regiment', volume 3, pages 186-233. (In the roster) (George W Rowan)
2 Civil War Veterans' Card File, available at the Pennsylvania State Archives, searched 29 June 2004 (George W Rowan)
3 index to compiled service records of volunteer Union soldiers who served in organizations from the state of Pennsylvania (George W Rowan)