Regularity means habit. If we can live, circumstance permitting, in a state of regularity in our daily life. We should be able to enjoy our healthy life as well as long life. But, to live a regular life, we need to build a habit upon which we can live our regularity easily.
Young people have more freedom to enjoy their life in a free style. They today can sleep at two am in the morning, but they can also go to bed at eight am in the evening tomorrow. They can do so without hurting their health.
But, once you come into middle age, you may feel that your energy is getting weak, unable to do things as easily as you did in your younger days. Sometimes, they may remember beautiful things in the old days, and they also fear what they will be in their future. Occasionally, they feel lost in this human world. For those people, they have to live in regularity or they will face illness of any kind.
For old people, all of them are forced to live their life in regularity, or they will die quicker. As no human wishes to die earlier if they have chance to live. Therefore, all old people have a habit of regularity in their life.