The technology required to cure aging is more difficult than the technology required to build food factories. The earth can support many more billions of people on far less land than we use today if there are investments into architecture and war/corruption is mitigated.
What is the point of that? Just have lots of people? That doesn't help anything. The whole idea of anti-aging is for individuals to live longer. Have their hard won expertise and skills continue to be of use longer, have them enjoy life more rather than a constant progression that ends in death.
That would be fine if we had a billion people on Earth, but whatever number ends up being stable, it's an orthogonal issue.
