Midrasch zu Wajikra 27:7

9) "For the male": and not a tumtum or a hermaphrodite. I might think they are not included in the category of "man," but they are included in the category of "woman"; it is, therefore, written (Vayikra 27:4) "And if she be a female" — either a definite male or a definite female, but not a tumtum or a hermaphrodite. And whence is it derived that the sixtieth year (itself) is regarded as below it? From (Vayikra 27:7) "And if from sixty years and above" — which teaches that the sixtieth year itself is (regarded) as below it.

11) Now if you make the sixtieth year "below it" for stringency (of liability) would you make the fifth year as the twentieth year "below it" for leniency (of liability)! It is, therefore, written "year" - "year" for a gezeirah shavah (identity) — Just as "year" written in respect to the sixtieth year is "below it," so "year" written in respect to the fifth year and the twentieth year is "below it" — whether for leniency or for stringency. R. Eliezer says; Whence is it derived that one month and one day (above the sixtieth year) is regarded as the sixtieth year? From (Vayikra 27:7) ("And if from sixty years) and above." It is written here "and above," and elsewhere (Bamidbar 3:15) "and above." Just as "and above" elsewhere is one month and one day after the month, so, here, one day and one month after the month is regarded as the sixtieth year.