Here's a few suggestions: 1) Try to correlate the ages of your grandmother on the various censuses.This should let you focus in on a birth year (or two or three). 2) Do you know what religion she was raised in, if any?Check the church records.If she was a Catholic, they tend to have great records, many of which you can find in the public libraries. 3) Find out where she was buried.The birth info may be in her headstone. 4) Find her death records.These may have birth info, as well. 5) See if anyone in your family kept a family Bible.A lot of times, birth info was scribbled on the first few pages, or on the last few. 6) Are none of your grandmother's siblings - your great aunts and uncles - still with us?Ask them if any are still around.Likewise, maybe a 2nd cousin - one of their kids - has info you might find useful.Tap all of these resources while you can. 7) Do you know the names of her parents?I assume not.But wives were generally married in the same counties or parishes that their parents lived in.Check out the families of anyone in the area with the same surname in the 1900, 1910, etc. censuses.Backtrack these families and locations.You may have to trace people that end up not being relatives, but chances are that you can find Granny with one of these families.Then backtrack that family.
You may end up never finding Granny's birthdate.But you may find a christening date, or something along those lines.This is almost as useful.