Date of Birth on Enrolment - Filter out

Is it possible to Validate the date of birth so as to prevent users under 18 (based on supplied birthdate) from enroling?>

For each Custom field there is a "Validation" option. If you set this value to "Past Date" you can manually modify the Validation Rules

for example

validate[required,custom[date],past[01-01-2000]]
Above line will indicate the Date of Birth must be before 1/1/2000

validate[required,custom[date],future[12-6-1986]]
Above line will indicate the Date of Birth must be after 6/12/1986

From what I know there is no option to base the value on the date of the event

I wonder if you could create a hidden form element to use the functionality of the validation "past" function:
posabsolute.github.io/jQuery-Validation-...nother-elements-name