I am new to EA, but it seems that a true effective altruist would not be interested in retiring. When just a $1000 can avert decades of disability-adjusted life years (years of suffering), I do not think it is fair to sit back and relax (even in your 70's) when you could still be earning to give.
Great work. I must admit that I am not very well read up on mental health, but it seems that the root cause of it is our lack of evolutionary fit with the current societal environment. To oversimplify, we aren't living in small tribes on the Savannah anymore. It seems to me like the most promising long term solution is genetic engineering us to be happier.