Could he be the same person as John T West, in company H?
He was 16 years old when he was enlisted (3).
He was enlisted and mustered into service on 3 September 1861 (1, 3). He was enlisted at Philadelphia, Pennsylvania (3). He was mustered in as a private, at Philadelphia, Pennsylvania (3). He served as a private in company D (1).
On 14 October 1862, he was discharged on writ of habeas corpus (1, 2, 3). However, if he was discharged because he was a minor (as seems likely), 14 October 1861 seems more likely.
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) (John B West)
2 company D, register of men discharged, entry 13 (John T [?] West)
3 Civil War Veterans' Card File, available at the Pennsylvania State Archives, searched 30 July 2004 (John B West)