1850 census of Bath Co., Ky, p. 30, lists as family #394:
Elizabeth Fielders, 55; James W. (or H.), 19; Thomas, 16; Julia A., 19. All born in Ky.
(Julia being listed out of age order may indicate that she is Thomas’s wife. But most likely she is the female age 5-9 in the 1840 census. If the age is correct, then she and James must be twins.)

Although Elizabeth is listed as 55 here (which is the basis upon which many family trees give her birthdate as 1795), her age was given as 20-29 in the 1830 census and 50-59 in the 1840 census. Probably she was born about 1800 or 1801, which would make her 29-30 in 1830, 39-40 in 1840, and 49-50 in 1850.

1830 census of Bath Co., Ky, p. 219, line 6:
William Fielder, 2 m < 5, 1 m 5-9, 1 m 30-39, 2 f < 5, 2 f 5-9, 1 f 20-29.

1840 census of Bath Co., Ky, district East of Slate Creek, p. 65, line 19:
Wm Fielder, 2 m 5-9, 1 m 10-14, 1 m 60-69, 1 f 5-9, 2 f 10-14, 1 f 15-29, 1 f 50-59.

This is the only William Fielder househould in both censuses, but William and his wife have both moved up three categories (30 years) in one decade. Most likely the marks are in the wrong columns in the 1840 census (a woman 50-59 is unlikely to have 3 children under 10), and they were at the very high end of the range in 1830 (a woman with 7 children is also not likely to be much under 30.) So I am estimating that William was born about 1790 and Elizabeth about 1800.