An ancestor is a person from whom a person is descended, e.g. parent, grandparent, great-grandparent.
When looking at deed indexes, be sure to look at both the Grantor Index, an index to those selling the land and the Grantee Index, an index to those buying the land.
To find a birth date from a death date, subtract the age in years, months and days from the date of death. This is a very close approximation.