A really ineresting way to look at aging is this: if longer life was evolutionarily advantageous, we would have evolved additional molecular mechanisms to support it. It's not that by dying earlier we keep the gene pool fitter, because that's not how evolution works. (We'd otherwise have a much more complicated algorithm on our hands.) Rather, we die simply because there is no advantage in having us persist--we only gained and conserved what was optimal for our species' lifecycle. Anything else requires extra energy and support machinery and is not likely to be amplified since occasional breakdowns are likely to be serious or fatal (and more common with the increased complexity!)

Compare gymnosperms (conifers) and certain angiosperms (flowering plants). The former persist for long periods under drought and stress conditions and only bear seeds after a two-year long development. Some desert angiosperms sprout, pollinate, spread seeds, then die in the span of a week. -- Different evolutionary strategies evolved under different environments and selection pressures.

(Concession: evolution isn't "optimal", but it has found good enough solutions that I often call it such.)