Cheryl, what is the source for the marriage date? I don’t see anything linked on familysearch or wikitree profiles for either. Trying to track it down some other way. Also, the 1850 census says he was 25, suggesting birth year of 1825. 1860 through 1880 seem to indicate birth year of 1820. The headstone that includes Mary J suggests he was born in 1815.
Is there a chance that the Jonathan & Mary in all those census records are not the same as the ones in that gravesite? Or do you think that the headstone date is inaccurate? The age gap between husband and wife changes from 3/5/9/10 years across the 1850 - 1880 censuses too. The ages and dates on the headstone would make Mary about 12 years younger.