Make National Identifier mandatory based on age of contact. If age>1 year, NID should be mandatory

Summary: We have a requirement for an autocomplete rule on Person Contact Relationship:

If the age of contact is greater than a year, then National Identifier should be a mandatory field on ESS>Family and Emergency Contact Page.

Content (required): Since age is not a delivered attribute, it has to be calculated on the autocomplete rule with the help of delivered functions and I need guidance as to what condition should be used in able to do so. If somebody has worked on a similar requirement, your help will be greatly appreciated.

Version (include the version you are using, if applicable):