Program.cs

public DateTime ConvertToDateTime()
{
    private static readonly string _dateString = "01 05 1991";
    
    var day = _dateString.Substring(0, 2);
    var month = _dateString.Substring(3, 2);
    var year = _dateString.Substring(6);
    return new DateTime(int.Parse(year), int.Parse(month), int.Parse(day));
}