It looks like this feature is already in there if I have both a birthday AND a year. I'd like to see the age if I only fill in a year (realizing it will be off by one before their actual birthday). This is helpful when my clients tell me their kids names and ages during a call, and I don't want to do the math going forward.

You could show ~13 years if it's just a year and 13 years if there's a birth date and a year.