Turtling might also involve a completely non-aggressive approach, that is you can only attack in defensive purposes. This way you can only win the game by making enough factions your protectorates and eventually sack Rome. Another more extrem form of turtling is the "City state scenario" where you abandon all settlements on the first turn and just keep one and you may not hold anymore settlements during the entire game. Try and win that game if you can, it´s extremely hard.