Sim 4: Start a new game with original households/sims

You can either start a new save file in the start screen if you don't want your original sims in your new game, and then you can switch between save files to play your different houses. Alternatively you can create a new household entirely and move them into a separate lot. If you don't want your original household to continue aging up, make sure you turn that option off in the Game Options (Menu>Game Options>Gameplay>Auto Age Played Sims - select no).

Hope that helps and welcome to The Sims!