Date calculations in Excel 2016 VBA

[ashgaroth]

' The following block of code calculates the service user's age and turns on the 'Child' radio button _
if the service user is under 18 years of age.
' This works fine in Excel 2007 but crashes out in Excel 2016 with a compile error (can't find project or library) on the highlighted line.
' It seems to me that it is due to the missing Calendar Control that does not appear to be available for the 64 bit version of Excel 2016. I could be wrong, of course, and welcome your comments.

                txtAge2 = vbNullString
                txtDOB2 = vbNullString
                If Range("N" & Cnt) > vbNullString And _
                    Range("N" & Cnt) <> "Not recorded on AIS" Then
                    'Call date_and_time(Range("N" & Cnt))
                    [highlight]txtDOB2.Value = Format(Range("N" & Cnt), "dd/mm/yyyy")[/highlight]
                    FirstDate = txtDOB2
                    SecondDate = Date
                    Age = Year(SecondDate) - Year(FirstDate)
                    Mth = Month(SecondDate) - Month(FirstDate)
                    Day1 = Day(SecondDate) - Day(FirstDate)
                    Select Case Mth
                       Case Is < 0
                           txtAge2 = Age - 1
                       Case 0
                           Select Case Day1
                               Case Is < 0
                                   txtAge2 = Age - 1
                               Case Else
                                   txtAge2 = Age
                               End Select
                        Case Else
                            txtAge2 = Age
                    End Select

                    If txtAge2 < 18 Then
                        opChild2.Value = True
                    Else
                        opChild2.Value = False
                    End If

                Else
                    txtDOB2 = ""
                    txtAge = vbNullString
                End If