[otrs] Delete old closed tickets

Hi all, I would like to delete all tickets which have state "closed" with their close-date older than X month. To achieve this I think I should use an generic agent job on all closed tickets, but how can it be checked that the close-date is minimum X month ago? I could call an external CMD that examines the DB-entries, but that's no good idea because this CMD-scripts need the DB-connection-parameters, an extra DB-connection etc., all thinks that are present within OTRS. So I think a self written module would be better. But I've no idea where to start ("25. Developer's guide - Writing OTRS Modules" on OTRS-DOC v1.3 doesn't really help me). Has anybody experience on that? Bye, Alex