If you've located your ancestor in census records that provide ages and places of birth, consider making a chart or somehow listing each year, what year of birth the age implies, and the place of birth.
How consistent are those years of birth? How consistent are those places of birth? A little variation is to be expected, but sometimes this can be a good way to realize that maybe you don't have the same person in all those records. Or maybe you do, but make certain you've got reasons for why you "know" it's the right person.