I'm thinking is there evidence that aging is actually part of the evolutionary process, and that it exists only due to this reason.
It’s part of the evolutionary process in the sense that aging is a physiological trait that has evolved in complexity in organisms through time. The aging process is intimately linked to metabolism and the immune system. This is why caloric restriction remains the most successful lifespan-increasing strategy for mammals (albeit not an attractive one).
In simple model organisms used in research, such as nematode worms (C.elegans) and fruit flies (Drosophila), there are a relatively small number of key genes that regulate aging. Thus, in these organisms, the genetic alteration of a single gene can have dramatic effects on lifespan and aging. For instance, mutations in the C.elegans
daf genes increase lifespan by ~2-fold (ie. from 2-3 weeks to ~5 weeks). Daf genes are part of an insulin-like signalling pathway.
When you move up to a more complex model organism such as the mouse you find a greater number of genes linked to aging in accordance with the more complex metabolic and immune systems of the mouse compared to flies/worms. Each of these genes on their own plays a much less significant role in aging. For instance, mice carrying the same mutations in the same genes as the C.elegans mutants display only an ~10-15% increase in lifespan at most (I think, from memory).
When you get to humans there are a very large number genetic polymorphisms associated with longevity, none of which on their own confer any measurable increase in lifespan. It’s not uncommon to find people on interweb forums who think that increasing human lifespan is merely a matter of tinkering with single genes as we do in flies and worms. Not so, not by a long shot.
Perhaps we can merely shut it off? What might happen to humanity if we all didn't age after 20 or 30?
We cannot do that and nothing I’ve ever read leads me to believe we will ever be able to do that. So that’s a purely hypothetical question that can be discussed in a sci-fi sort of way.