Walking is the best exercise for everybody, but walking up hill is the best of bests. The reason is simple. By walking on the street, you will not get sweating, yet, if you walk up to the peak, your body will be automatically sweating by which poison in all organs of your body is releasing out and you will feel much better in your daily life.
Young man can walk up hill very fast because their heart is strong and elastic, but for middle aged people, too fast walk to hill will certainly harm their hearts in an invisible way. For old persons, fast walk is definitely to be avoided, violating which will bring them disaster in different consequence either to go to hospital to have emergency care or, to the worst case, the patient may die.
To go to peak should be best early in the morning. It is at this period that the air is fresh and you can breath as much fresh air as you can to digest dust from your lung.
Up to peak can increase your muscle as well, increasing body resistance, and illness will not fall upon you basically.
But, if you like to go to peak for your exercise, it is better to go every morning. It can be sure that you will have a good health if you persist this exercise.