Is there a way to add an option to limit the birthdate field to only accept dates equal to or earlier than the current date?

We do not accept applications for children yet to be born and as we do not operate on a first come first served basis, there is no value to parents eg booking an open event this early. A lot can happen in 3 years (between (successful) birth and assessment for entry) and parents receive outdated and potentially misleading information should they visit too soon.