There isn't really an ideal body fat percentage. We come in all shapes and sizes. However, extremely high levels of body fat are correlated with poor health outcomes. Likewise, extremely low levels of body fat can cause problems. As a rough approximation the majority of women will probably get the best balance of health and body composition somewhere between 17-22% body fat. As we age these number are prone to increase due to a loss of muscle mass. Regular resistance training is the best bet to stall and fend off this natural decline.