Animal Charity Evaluators makes sense because of a values difference: they provide recommendations for people who prioritize animals much more than is typical. I don't think there's something similar with anti-aging; it's just that GiveWell's not yet in a position to evaluate more researchy organizations, though this is changing as the Open Philanthropy Project progresses.

(I do think a GiveWell competitor would be valuable, but in the cause-neutral sense of one looking at all the potential funding-constrained altruistic options and picking the best ones.)