I'm a complete novice but slowly getting there with mail merge.

I'm trying to use mail merge with microsoft word. I've created a letter and successfully added a name field, date of birth field, today's date field. Those fields are showing the correct information on my letter now.

The field I really want now is an age in years and months field.
E.g.
Date of birth: 21/08/2000
Age: 13.10

The age would show something similar to above, the age in years followed by the number of full months. It it possible for something like this or something similar?