>It seems like there would be some advantage to some creatures of not aging, or having individuals who have significant longer life spans.

There is, if there were no advantage a whole lot more species would die immediately after reproduction like the octopus.

Many simpler organisms are vaguely immortal.

>It's easy to imagine a world where nature might want to keep the alpha lion around longer than the others so it can have more offspring, for example.

The utility of genetic diversity puts a lot of pressure against this.