Based on the rate at which medicine is evolving, the answer to this question is a resounding “Now!”
Almost every disease has a cure or a cure-in-testing, and aging is just one of those diseases.
In the book How To Live Forever, I wrote four sections on ways that we already know to slow or even reverse aging, including telomere extension, senolytics such as FOXO4-DRI or UBX0101, calorie restriction, and increasing NAD+.
Of the four, three of them are in human trial at the moment, and the fourth has already been shown to reduce the incidence of tumours in humans.
Telomere extension has already been shown by Elizabeth Parrish to increase telomere length by 9%. This equates to about 10-15 years of life extension. This year, it was shown that telomere extension treatment in progeria sufferers results in decreased inflammation and decreased β-galactosidase almost immediately after treatment. Because humans live so long, it is hard to know for sure if live extension works. Progeria is basically a disease that increases the speed of aging in humans – if you can slow or cure progeria, there’s a good chance you’ve also made huge steps towards curing aging itself.
Senolytics are drugs that kill senescent cells – cells that have stopped replicating and producing new young cells, but which also refuse to die. Instead, they stick around spewing out inflammation proteins and causing other nearby cells to also go senescent, resulting in more and more of your cell population becoming old and useless. Senolytics such as FOXO4-DRI or UBX0101 work by covering the part of the FOXO4 gene which is stopping the cell from dying, thus forcing the cell into apoptosis (cell death), making room for new young cells.
Calorie restriction is shown in lab animals to reduce the incidence of tumours (cancers), and leading to longer (up to 50% longer!) lives as a consequence.
And finally, NAD+ is a catalyst which helps the mitochondria of your cells to work with oxygen to produce energy. In older people, the amount of NAD+ in your cells reduces, making it harder for the cell to produce energy, and sometimes resulting in DNA-replication errors. To increase NAD+ in your cells, you can either inject NAD+ directly, or ingest NMN (a precursor molecule that turns into NAD+ in the body).
There are a lot of other methods of living forever, but these are the big four at the moment.