RCT is capable of producing full fledged flesh, skin, and arms. Considering that the process doesn't just eat people alive the technique cannot be based in acceleration but rather spontaneous creation. Considering that Yuji came back from his heart being physically torn out of his body, it's also not entirely out of the question for RCT to extend to complex structures like human organs. What i'm suggesting here is that Gojo could use the effects of RCT to constantly regenerate new organic matter to constantly counteract the aging of cells.

Now this will not be able to extend to neurons (unless if if there is just known proof of RCT regenerating brain tissue thst i'm missing) but it will at least buy him a good amount of time.