Aging is a natural process that happens to all incarnated entities, although the rate and effect may differ. Let us be specific. Complex organisms fight two battles. One is to gain in size and complexity soon enough to reproduce effectively, and the second is to stave off the aging process while this is going on. What is the aging process? Any machine wears down, the edges of the parts getting rough until they fail to operate as expected, connections breaking, refurbishments failing to appear when needed, and foundations crumbling under weight over time. Happens everywhere, all the time. Happens to the intelligent, conscious, bodies incarnated with indestructible souls. But there are pros and cons, and there are differences in the aging process between the densities and between intelligent species on other worlds. Aging is a factor of other matters.
In higher densities aging takes place more slowly, as the physical body has less weight than the spiritual body. This is to say that the faults in the physical body are amended by the spiritual, which wishes to remain in the body for as long as possible. The spirit steps in and acts as a bridge at the points where the physical body is failing, taking up some of its time and energy to do so, we might add. On some worlds aging takes place less drastically, as the shape of the physical body is such that simplicity prevails. Take the simple VW bug, which runs forever because it has few parts simply structured. Same principle.
For those wishing to defer the aging process as long as possible, the following advice is given. Think of all parts of the body as important, not just those that complain loudly. The kidneys and liver operate quietly, and get nowhere near as much attention as the clogging arteries or laboring lungs, which alert their host by pained legs and chest or short breath. Yet these organs cause quiet destruction, not yet known to your physicians. Drink lots of clear water, or fluid filled meals, as the primitive animals that were your precursors ran a continuous race, sweated much, and required lots of fluids. Do not overburden your livers with rich meals, which some of your number deliver daily. Rich meals were a rarity among the primitive animals which were your precursors, a feast they had only when a large animal was downed and competition for the kill scarce. The liver needs to spring back, but the treatment frequently given by civilized man is like the continuous punching that referees in the boxing ring don't allow. Time out!