how to calculate age by using calender tool

Private Sub deDOB_EditValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles deDOB.EditValueChanged
        Dim years As Long

        Select Case Today.Month
            Case Is < deDOB.DateTime.Month
                years = DateDiff(DateInterval.Year, deDOB.DateTime, Today) - 1

            Case Is = deDOB.DateTime.Month
                Select Case Today.Day
                    Case Is < deDOB.DateTime.Day
                        years = DateDiff(DateInterval.Year, deDOB.DateTime, Today) - 1
                    Case Is = deDOB.DateTime.Day
                        years = DateDiff(DateInterval.Year, deDOB.DateTime, Today)
                    Case Is > deDOB.DateTime.Day
                        years = DateDiff(DateInterval.Year, deDOB.DateTime, Today)
                End Select
            Case Is > deDOB.DateTime.Month
                years = DateDiff(DateInterval.Year, deDOB.DateTime, Today)
        End Select

        txtAge.Text = years.ToString
    End Sub