Birthday Validation appears to be about a month off.

[raalin19]

I'm trying to validate a birthday being over 21 years of age.
I've set the following options on the input:

data-validation="required date birthdate"
data-validation-format="mm/dd/yyyy"
data-validation-age-range="21-124"
data-validation-error-msg-date="Please enter a valid date MM/DD/YYYY"
data-validation-error-msg-format="Please enter a valid date MM/DD/YYYY"
data-validation-error-msg-required="Please enter your date of birth."
data-validation-error-msg-birthdate="You must be 21 or over to register."

For the most part it appears to work correctly, however it is about 28 days off.
For example today is 08/07/2017
Entering 08/06/1996 triggers an error and displays the 'correct' message.
Entering anything on or before 07/07/1996 succeeds, but 07/08/1996 also proves to be invalid.

Any advice?