I’ve seen studies on this idea, it involves genetic changes to living humans, probably carried out in the womb, which would remove our genetic predisposition to die. Crocodiles and other primitive reptiles have this property, they go on living and growing until they die of natural causes. Hormones could then be added to induce puberty so we’d stop growing but would not grow old.
Even if you eliminated old age, this would not mean everlasting bodily life. Only a small number of people die of direct consequences of old age. If you cured all diseases AND eliminated old age, that would still leave death by accidental cause, which accounts for around 6% of deaths at present, which means an average lifespan around 900, the same as the Old Testament patriarchs, but it would not be a guarantee of any particular age. One man could live to be 3000, but a 5-year-old could still get hit by a car and killed.
Other than the existing prescriptions against IVF and embryo research, this would also contravene other existing Church teachings.
For example, our organs only have a projected lifespan of about 120 years, so after that we would have to grow modified embryos to be organ-bags for the living. With a population that lived that long, serious limits would have to be placed on reproduction, probably leading to mass sterilizations.
It’s not a recipe for living forever, it’s a recipe for a very protracted death and stagnation, with very few new lives being brought into existence. It’s very selfish technology indeed. I think if they had time to think it through, most people would rather have death than the alternative.