The rationalist and effective altruism communities overlap to a considerable degree, and do engage with the goal of radical life extension through the development of rejuvenation therapies, but not to the degree that I think would be rational. The only rational use for excess capital in this day and age is purchasing an acceleration in the development of rejuvenation biotechnology, on the grounds being alive and healthy enables all other options. That acceleration can be achieved through philanthropy, via support of the SENS Research Foundation, Methuselah Foundation, and similar organizations, or via investment in startups focused on the development rejuvenation therapies. But it can be achieved, and that is perhaps the point that hasn't yet sunk in in a large enough fraction of people.
As our ability to affect the aging processes has been dramatically improved within the past decade, now is an excellent time for rationalists to consider new evidence regarding the necessity and feasibility of rejuvenation biotechnology. The amount of harm caused by aging is immense from a human standpoint. It is, by far, the greatest threat to living people today, even in the most violent of countries. (It has long since dethroned the previous all-time killer, infectious disease, which we did something about.) In a world with untreated aging, everyone who does not die of something else will suffer from decades of declining health. Death is the inevitable result.
Aging is a global tragedy from an economic standpoint as well. Aging is the largest driver of healthcare costs in the United States. As birthrates remain low and unhealthy lifespans remain relatively long, the proportion of the economy devoted to taking care of older people can only increase. This economic burden represents an enormous expenditure of human labor, as large amounts of money and time are spent on keeping people alive as their bodies slowly fail them.
Fifteen years ago, the idea of intervening against aging through rejuvenation biotechnology was widely considered unfeasible or outside of human ability; today, it is mainstream science. The Hallmarks of Aging is one of the most frequently cited papers in biology. A wide variety of researchers at prestigious universities are actively involved in pursuing rejuvenation biotechnology therapies. Multiple biotechnology companies are developing interventions against the Hallmarks of Aging, each one of which has at least one partial intervention currently in development. For any given person, it is possible that partial interventions may delay enough of the aging processes long enough for further interventions to allow for more healthy years of life, until, ultimately, a comprehensive suite of therapies is developed to control all of the aging processes. This concept is called longevity escape velocity.
Unfortunately, aging is an enormous problem, not just in terms of the harms it does but in the number of specific therapies that will need to be successfully developed in order to completely control it. The current amount of effort is significant but not enough to bring about the medical control of aging as soon as would otherwise be possible. As a rationalist, you know better than to suffer from the bystander effect, waiting for someone else to do what needs doing. If you have the aptitude and are entering college, consider becoming a researcher yourself. Alternatively, you can aid advocacy efforts, fund research efforts, or, if you are an investor, finance the development of rejuvenation biotechnology companies.