Well, at first glance this looks very feasable. There is definately a Frankford connection. I have a citation for marriage to Uretta Zigler Jan. 1858. This would be about a year prior to Isaac's birth. David B. would have been about 16 years old at that time. It is a bit unusual but possible, I guess. Also, it puts Isaac's birth about two years earlier than reported on the 1880 census.

Could it be that Hulda (Isaac's stepmother) didn't know exactly how old Isaac was?