Well people have issues with living for a long time if their loved ones died and religion is also a part in why others won't support this. It's not immortality as he said and for when to choose what time of life u want to slow down aging should be to the patient recieving the treatment.
What i find really irritating are extremely religous people that wouldn't hear it just beleave in whatever they do and say thats all that exists. Most people have fears that if they live longer they might be murdered violently instead of dying from regular issues. But if people don't want to be apart of this they don't have to it's not gonna be forced down their throats.
Anti-aging reminds me of the Hydra(metazoen) that has escaped Senescence if we could find ways of expanding research on the Hydra and incorporate it into de Grey's idea.