'Sixty' in the Bible

'And if a female she bear, then she hath been unclean two weeks, as in her separation; and sixty and six days she doth abide for the blood of her cleansing.

And thy estimation shall be of the male from twenty years old even unto sixty years old, even thy estimation shall be fifty shekels of silver, after the shekel of the sanctuary.

And if it be from sixty years old and above; if it be a male, then thy estimation shall be fifteen shekels, and for the female ten shekels.