Reference for Bekhorot 97:20
ומשום הכי מספקינן ליה
For since it was necessary to write 'and upward' in connection with the law of valuation<span class="x" onmousemove="('comment',' And if it be from sixty years old and upward (Lev. XXVII, 7) . And in Tractate Ar. we draw an analogy between the expression 'year' used here and the 'year' mentioned in the same chapter in connection with the valuation of one twenty-five years old, to the effect that just as in the former case a valuation exactly on the sixtieth birthday is regarded as a valuation under that period, where it makes the person liable to a larger sum, similarly a valuation exactly on the twenty-fifth birthday is regarded as a valuation under that period, although it means paying a smaller sum of money for the person thus valued. The same principle also applies to the valuation of a child on the thirtieth day, the thirtieth day being counted like the previous day, although this means taking a lenient decision, and we do not draw the analogy between the expressions month used with reference to valuation and month used in the Book of Numbers so that there should be no valuation until after it is thirty days old');"><sup>18</sup></span>