I have already answered a similar question, I will add something, and I will quote something. Indeed, the aging process itself, with its inevitable degradation, decrepitude and helplessness, is like a mockery of nature over organisms. Nature has a mechanism of "programmed death" (apoptosis, phenoptosis)
when an individual dies instantly giving offspring or for any other reason, but not from old age. So why, after all, did nature come up with aging? There are certainly many answers to this question, from a peculiar control over the number to an equally exotic way, thus, to accumulate and transmit "the necessary mutations". If we talk about the processes themselves leading to aging, then there is no single point of view, there is an indication of a set of interrelated causes. At the cellular level, we are talking about mitochondria and their death under the influence of accumulated free radicals. This leads to the fact that the cell begins to experience a lack of energy for normal functioning and, relatively speaking, "grows old". There is a problem with telomeres and it is as follows. Telomeres, along with the "protection" of chromosomes, are needed for the normal DNA replication process to proceed. That is, roughly speaking, with each replication, a small part of the telomere is "lost" and when the telomere is shortened, a special mechanism is completely triggered and the cell stops dividing and becomes senescent. Here I would like to add that now they want to enhance the work of telomerase, an enzyme that "completes" telomeres, but there is a possibility that cancer cells use just such a mechanism, and this must be remembered. But even here there is one nuance, in the "old" organism there are about 20% of "young" cells, and some cells of the body do not divide at all, therefore the Hayflick limit of 50 + -10 cell divisions does not give an exhaustive understanding of the issue. Various kinds of mutations in genes and their influence on the functioning of certain body systems are also likely to contribute to aging. It should also be added here that failures in the hypothalamus-endocrine glands system certainly also contribute to aging. In short, everything seems to be clear about how aging occurs, but why organisms age is not yet clear.
I didn’t find any normal answers on the site, except this thread: thequestion.ru. First I think it is worth dismissing part of the question "How did evolution allow this?", because evolution does not allow anything. Evolution is not a magical power that improves creatures. Evolution is the process by which creatures with certain mutations are more adapted to environmental conditions than other members of their species. Such creatures have a better chance of survival and often their genes are dominant, due to which their mutations spread faster throughout their species, cutting off the previous "version". Animals look this way because others are extinct, not because evolution magically created and adapted them. Evolution is a random process of mutation.
Now about aging: aging in most living organisms is caused by the shortening of telomeres at the ends of chromosomes.