type
  String40 = string;

type
  TPerson = class
  private
    FFirstName = String40;
  published
    FirstName: string40 read FFirstName write FFirstName;
  end;

var
  MyPropInfo: TPropInfo;
  PropTypeName: string;
  MyPerson: TPerson;
begin
  MyPerson := TPerson.Create;
  MyPropInfo := GetPropInfo(MyPerson, 'FirstName')^;
  PropTypeName := MyPropInfo.PropType^.Name;

type
  String40 = type string;

program Project1;

uses
  Classes,
  typInfo,
  Dialogs,
  Forms;

{$R *.RES}

type
  String40 = type string;
  TPerson = class(TPersistent)
  private
    FFirstName: String40;
  published
    property FirstName: string40 read FFirstName write FFirstName;
  end;

var
  MyPropInfo: TPropInfo;
  PropTypeName: string;
  MyPerson: TPerson;

begin
  Application.Initialize;
  MyPerson := TPerson.Create;
  MyPropInfo := GetPropInfo(MyPerson, 'FirstName')^;
  PropTypeName := MyPropInfo.PropType^.Name;
  ShowMessage(PropTypeName);
end.

type
  String40 = type string;
  TPerson = class
  private
    FFirstName : String40;
  published
    property FirstName: string40 read FFirstName write FFirstName;
  end;

var
  MyPropInfo: PPropInfo;
  PropTypeName: string;
  MyPerson: TPerson;
begin
  MyPerson := TPerson.Create;
  try
    MyPerson.FirstName := 'My first name';
    MyPropInfo := GetPropInfo(MyPerson, 'FirstName');
    if MyPropInfo<>nil then begin
      PropTypeName := MyPropInfo^.PropType^.Name;
      Memo1.Lines.Add(PropTypeName);
    end;
  finally
    MyPerson.FRee;
  end;
end;