Validation Rule and Calculating age from date

I need to create a validation rule checking a data element if has a value of Yes and if the age calculated from a date is less than 18 years. I then I need to display a warning.

I went to add a validation rule and for the left side expression, I’ve added the first field==“Yes”, but can’t calculate the age from a date.

So how to calculate the age from date and should I add a right side expression too ?