Magento 2: Customer account create Date of Birth field seprate dropdown

I have to add Date of Birth as a seprate dorpdown DD MM YYYY formate in customer account create form and my account section.

I have implement dob.phtml and dob-validation-dropdown.js but not saving data, when submit create account form getting error.

Error:

ValueError: bcsub(): Argument #1 ($num1) is not well-formed in
/var/www/html/magento24/vendor/magento/zendframework1/library/Zend/Locale/Math.php:259
Stack trace:
#0 /var/www/html/magento24/vendor/magento/zendframework1/library/Zend/Locale/Math.php(259):
bcsub()
#1 /var/www/html/magento24/vendor/magento/zendframework1/library/Zend/Locale/Format.php(385):
Zend_Locale_Math::Sub()
#2 /var/www/html/magento24/vendor/magento/zendframework1/library/Zend/Locale/Format.php(662):
Zend_Locale_Format::toNumber()