Each of the other answers address some aspect of the issue, and it is far more complex than any of them indicate.
Yes, there is an aspect to it that the effect of deleterious mutations later in life is less if it happens after reproduction happens. And when considering that, one has to consider the entire environment of reproduction, which includes raising individuals in communities to a level that all the knowledge embodied in the stories and traditions of that community can be passed on – so not a simple metric.
Yes, there is an aspect that evolution is about reproduction and differential survival of variants in different contexts. And evolution quite quickly becomes much more than just that, as many levels of “strategy” emerge and become significant influences on survival.
If you consider that everything alive today, from the simplest bacteria, to plants, animals, us; appear most probably to be all equally the result of evolution on this planet from a single common cellular ancestor some 4 billion years ago, then one can start to see just how big an influence context has on what evolves.
The default mode for cellular life is indefinite life.
Cells do not, by default, lose function as they age.
Bacteria divide in two when they reach a certain size. Which of those two is the original? Each would (if it could, which it can’t) consider itself to be the original one.
Thus there is a very real sense in which all cells alive today can be thought of as the original cell changed by the particular context of its existence through time.
Considered that way, it becomes obvious that age related senescence (loss of function) is a genetically acquired characteristic that has led to the evolution of more complex life forms (as the life forms without it are still much simpler).
So when one looks at aging in this context, where one is dealing with the survival of sexually reproducing populations of individuals (which populations can at one level be considered as individuals for evolutionary purposes, just as we consider ourselves to be individuals even though from a cellular perspective we are a cooperating colony of trillions of cells), one can see that limiting the life expectancy of individuals within a population allows for the population to adapt far more quickly, and develop far greater levels of complexity, than populations of individuals that are not so limited. The mathematics and logic for that are far from simple, and apply only to sexually reproducing populations.
We are far from simple.
Even the simplest human being embodies at least 15 levels of complex cooperative systems.
For species like ourselves, it is far more accurate to say that evolution is all about cooperation, than to say evolution is all about competition.
For bacteria, evolution is much more nearly all about competition, that is why they are still simple bacteria.
The sort of complexity that we are is predicated on multiple levels of cooperation.
To a good first order approximation, our survival demands cooperation at all levels. The idea that many have, that evolution is all about competition, is, in respect of organisms like ourselves, essentially wrong.
And we are much more complex than simple ideas like cooperation verses competition can possibly express.
Our survival as a species is also predicated on the spectrum of diversity that we see in all the different spectra present (emotions, personalities, sociality, conservative-liberal, intellectual ability, etc). We need that diversity, and pretending otherwise dooms us to extinction. Every individual is more complex than even the most intellectual is capable of appreciating in detail, and as such demands respect and tolerance.
So to be able to understand the evolution of aging, and to be able to see the need in our present technological and social reality to go beyond aging, and once again extend indefinitely the life of individuals (at a level beyond cell), one needs to be able to appreciate levels of complexity that very few people have the time or inclination or innate ability to investigate and comprehend.
One of the things that 50 years of interest in evolution has taught me, is that if you cannot see how efficient evolution is, then you are not looking at it through the most appropriate context.
Aging was efficient in the context of our development to this point.
Our exponentially changing intellectual and technological context has made that no longer the case.
That reality will be very difficult for people on the more conservative end of the spectrum to comprehend and appreciate. That is a risk that evolution has not previously encountered at this sort of level.
We are in new territory.
This is seriously non-trivial complexity, and it seems clear to me beyond any shadow of reasonable doubt that the survival of all of us in now predicated on both universal cooperation and individual life extension.
Market metrics of value are no longer suitable tools for future planning – we have passed that threshold.