Generally speaking, there are two types of being fit. If your five basic motoric skills, naming stamina, strength, speed, mobility and coordination, are well-balanced, you are physically fit. And if you have a balanced diet, can concentrate and relax easily and sleep deeply you are mentally fit. Ideally, fitness should be achieved through little everyday trivialities and be optimized with targeted training. At least 30 minutes per day or not more than 4-5 hours per week are necessary to maintain fit.
There are even studies saying that fitness increases productivity and experts assuming that our brain can get bigger through fitness. Other advantages of fitness are that your circulation maintain in full swing and that it assists our concentration which further lifts our mood. It is also said that active people are less fragile of getting depressions. Especially for older people, doing fitness is advantageous.
If you get older your motoric skills slowly reduce and fitness is preventing such process. The sense of balance is being trained, muscles are getting smeared and stabilized and in general the control over your body gets better. With all that in mind, fitness can protect older people from easily tumbling. It also has anti-ageing effect, since fitness is encouraging our blood flow which lets our skin appear younger.