The ideal fat ratio according to age will vary depending on a person's lifestyle, fitness level, and health goals. Generally, for adults aged 20-40, a healthy fat ratio should be between 25%-35%. For those over 40, a healthy fat ratio should be between 20%-30%. However, it is important to note that these numbers can vary for each individual, depending on their individual goals and lifestyle. For example, an athlete may have a higher fat ratio than the recommended values, while someone looking to lose weight may have a lower fat ratio. Ultimately, the best fat ratio for each individual is one that promotes health and meets their individual lifestyle and fitness goals.