The simulation argument is definitely true, in the sense that one of the outcomes Bostrom describes must be true. I don't think he takes a position on which outcome is true, so I'm not sure what there is to disagree with there.

As for aging and life extension, I honestly don't understand how anyone could reasonably think we shouldn't stop or reverse aging.

Those are some bold claims that not even Bostrom makes. Irregardless, I would take one but for a fool for assertions without the backing of evidence: of which a hypothetical thought-experiment is not.

I can certainly comprehend why one would wish to become an immortal being incapable of death. But I just want to be human. Sure you can live forever, but at what cost? A fear for sunlight, garlic, and crosses? For me, "Death is very likely the single best invention of Life."