Option Compare Database
Option Explicit

Public Function Age(Arg_BirthDay, Optional Arg_BaseDay) As Variant
Dim tmpBirthDay As Date
Dim tmpBaseDay As Date

Age = Null
If IsMissing(Arg_BaseDay) Then
　Arg_BaseDay = Date
End If

If IsNull(Arg_BirthDay) Or IsNull(Arg_BaseDay) Then
　Exit Function
End If
If Not (IsDate(Arg_BirthDay) And IsDate(Arg_BaseDay)) Then
　Exit Function
End If
If VarType(Arg_BirthDay) <> vbDate Then
　tmpBirthDay = DateValue(Arg_BirthDay)
Else
　tmpBirthDay = Arg_BirthDay
End If
If VarType(Arg_BaseDay) <> vbDate Then
　tmpBaseDay = DateValue(Arg_BaseDay)
Else
　tmpBaseDay = Arg_BaseDay
End If

If tmpBirthDay > tmpBaseDay Then
　Exit Function
End If

If Format(tmpBaseDay, “mmdd”) < Format(tmpBirthDay, “mmdd”) Then
　　Age = Year(tmpBaseDay) - Year(tmpBirthDay) - 1
Else
　　Age = Year(tmpBaseDay) - Year(tmpBirthDay)
End If
End Function