Automatic Age Calculation in Word Document

It is pretty simple with a macro:

Sub TestDetailed()
  'MsgBox fcnCalcAge(InputBox("Enter birth date in ""MM/dd/yyyy"" formmat", "Birth Date"), Now)
  MsgBox fcnCalcAge("12/31/1958 4:34", Now)
End Sub

Function fcnCalcAge(oDateBD As Date, oDateNow As Date, Optional ShowAll As Boolean = False, Optional Grammar As Boolean = True)
Dim lngYear As Long, lngMonth As Long, lngDay As Long
Dim oDateLDPM As Date, oDateLDIM As Date, oAnchorDate As Date
     
  'Restrict to date only (i.e., no 12/31/1958 3:15 p.m.)
  oDateBD = Int(oDateBD)
  oDateNow = Int(oDateNow)
  'Limit to to persons already borned.
  If oDateBD > oDateNow Then
    fcnCalcAge = "Come back after your birth date."
    Exit Function
  End If
  'Calculate complete years passed.
  If Year(oDateNow) > Year(oDateBD) Then
    'A different calendar year. Has one or more complete years passed?
    If Month(oDateNow) = Month(oDateBD) Then
      'Same month in subsequent year. Check day.
      If Day(oDateNow) >= Day(oDateBD) Then
        'Complete year passed
        lngYear = DateDiff("yyyy", oDateBD, oDateNow)
      Else
        'e.g, birthdate 6/14/2000, date now 6/13/2015 returns fourteen years.
        lngYear = DateDiff("yyyy", oDateBD, oDateNow) - 1
      End If
    ElseIf Month(oDateNow) > Month(oDateBD) Then
      'Complete year passed.
      lngYear = DateDiff("yyyy", oDateBD, oDateNow)
    Else
      'e.g, birthdate 7/13/2000, date now 6/13/2015 returns fourteen years.
      lngYear = DateDiff("yyyy", oDateBD, oDateNow) - 1
    End If
  Else
    'Obviously no complete year passed.
    lngYear = 0
  End If
  'Calculate full months passed from last full year.
  lngMonth = (DateDiff("m", DateSerial(Year(oDateBD), Month(oDateBD), 1), _
              DateSerial(Year(oDateNow), Month(oDateNow), 1)) + IIf(Day(oDateNow) >= Day(oDateBD), 0, -1)) Mod 12
  'Calculate number of days passed from last full month.
  If Day(oDateNow) >= Day(oDateBD) Then
    lngDay = Day(oDateNow) - Day(oDateBD)
  Else
    'Calculate for end of month.
    'Get date on last day of previous month.
    oDateLDPM = DateSerial(Year(oDateNow), Month(oDateNow), 0)
    'Get date on last day of index month.
    oDateLDIM = DateSerial(Year(oDateNow), Month(oDateNow) + 1, 0)
    oAnchorDate = DateSerial(Year(oDateNow), Month(oDateNow) - 1, Day(oDateBD))
    If oDateLDIM = oDateNow Then
      If lngMonth = 11 Then
        'Reset month and add a year.
        lngMonth = 0
        lngYear = lngYear + 1
      Else
        lngMonth = lngMonth + 1
      End If
    Else
      lngDay = DateDiff("d", IIf(oAnchorDate > oDateLDPM, oDateLDPM, oAnchorDate), oDateNow)
    End If
  End If
  If lngYear >= 1 Then
    fcnCalcAge = lngYear & IIf(lngYear = 1, " year, ", " years, ") & lngMonth & IIf(lngMonth = 1, " month, ", _
                 " months, ") & lngDay & IIf(lngDay = 1, " day", " days")
  Else
    If lngMonth >= 1 Then
       fcnCalcAge = lngMonth & IIf(lngMonth = 1, " month, ", " months, ") & lngDay & IIf(lngDay = 1, " day", " days")
    Else
       fcnCalcAge = lngDay & IIf(lngDay = 1, " day", " days")
    End If
  End If
lbl_Exit:
  Exit Function
End Function