I haven't seen another Isaac Townsley close to that age in the census. 1900 census states - date of birth Feb. 1845, but I've seen countless times where there's a year difference from tombstone date and 1900 date.
His family was living in the middle of Missouri during the time period (1861-1865). Ohio County, Ky is not exactly close to Ohio, nor Missouri. He had a rather unusual path to the 2nd Ohio Cavalry. Was Ohio offering a good incentive in 1864?
1900 Precinct 3 Astoria City Ward 1, Clatsop, Oregon
Isaac N Townsley....55....TN....VA...VA....Photographer
1920 Sulphur Ward 2, Murray, Oklahoma
Isaac N Townsley...74...TN...Carolina...Carolina.....Photographic Studio
1930 Checotah, McIntosh, Oklahoma (Odd Fellow Home)
I. N. Townsley....85...TN....US...US