Preamble: I am an atheist. So I don’t have any God-related issues concerning rejuvenation/living forever. Other people, though, may believe there’s an afterlife waiting for them once they die, or that curing ageing equals playing God. I don’t think these are particularly problematic concerns.
First, if anyone at all, believer or not, wishes to die at any point, I am in no position to object. It’s their life, not mine, and they can do with it whatever they see fit. If you are afraid of never reaching your god because of quasi-immortality, I think you should be free to die the way you wish, be it by ageing or whatever way you prefer (as long as you don’t take others down with you). I think it’d be crazy to terminate your life for this reason, but hey, whatever
sinks floats your boat. It’s your choice, and you should be given it. Rejuvenation isn’t about forcing people to never die. It’s about giving them the possibility of living in perfect health for as long as they see fit.
Speaking of the ‘playing God’ problem, I think the real problem is one of definition. What does ‘playing God’ mean? Is it defined anywhere in your holy book? Why is curing ageing ‘playing God’, but curing diseases isn’t? We have already established that curing ageing doesn’t make you immortal. Rejuvenation isn’t about throwing a challenge to your god. It’s about putting an end to people’s suffering, which I understand gods generally appreciate. (When they aren’t in the mood for plagues anyway.) If your god is almighty and all-knowing as you probably think it is, I’m sure it will take your life and everyone else’s whenever it sees fit anyway. I wouldn’t be afraid of its judgement after your death: If you supported rejuvenation, you supported a cause that prevented people’s suffering, including your own. That’s pretty damn noble.
Finally, whether somebody lives or dies, religious people generally interpret this as God’s will. If a man is very sick and doctors can’t save him, after his death believers will likely say that God decided his time had come. However, if doctors were able to save the man, then believers will likely thank God for deciding to save his life. So, either way, it is God’s will. If in a few decades doctors will be able to save people from ageing, maybe this is God’s will too. For all we know, he might have specifically arranged things so that rejuvenation is created at a certain point in time. He might have had some reason beyond our understanding to call to himself all people prior to a certain point, and save the lives of everyone after it. This point might be the moment rejuvenation becomes real. Of course, as an atheist, I am extremely sceptical about it, but if you are a believer, this might make sense to you.
Objections to living ‘forever’
Objections to rejuvenation
All answers in short