type
  TRegistrationFee = class(TPercentCalculated)
  public
    class function New(
      OriginalValue: Currency): IMoney;
  end;

  TDiscountRate = class(TPercentCalculated)
  public
    class function New(
      OriginalValue: Currency;
      Birthday: TDateTime): IMoney;
  end;

implementation

class function TRegistrationFee.New(
  OriginalValue: Currency): IMoney;
begin
  Result := inherited Create(OriginalValue, 1);
end;

class function TDiscountRate.New(
  OriginalValue: Currency;
  Birthday: TDateTime): IMoney;
begin
  Result := inherited Create(
    OriginalValue,
    TIf.New(
      (Now - Birthday) < 18,
      10,
      0
    ).AsCurrency
  );
end;

end.