I recommend to "separate" past events by creating a new/additional category for them, named i.e. "archived".
In backend events management, you only see present and upcoming events (default). In frontend-calendars, you can exclude past events from being displayed or exclude categories ("archived"). In the frontend list-views, only present and upcoming events are displaying.
Further advantage of a using a category: you can create a CiviRule to automatically assign/unassign the respective categories once the event is x days/hours/months in the past.