Mantainance is already covered efficiently by the different systems/apharatus and the respective cells's inner working. It's practically a system with such a low failure probability, that (talking in vague words) isn't primarily responsible for aging process.

Surely the acceleration of certain reactions that tend to cell division, increases the probability of mutations which induce "errors". Yet almost every cell in your body also has a plenty (like 8) mechanisms at DNA level, to prevent such things to happen. And quite a few more at RNA and Protein levels. (E.g: checking if protein is folded properly, then folding it as it should or simply degrading it).

Do they happen from time to time? Yes. But remember we also have the inmmune system, which more specifically the natural immunity one, and more specifically the monocyte-macrophage system, involved in recognizing rare local cells with uncommon markers and fagocitating ("eating them") if recognized.

So, in the end we have a whole lot of barriers that prevent such things to happen. So, phisiologically (aka normal) metabolism isn't much of the problem here.

If you assume cathastropic theory, aging is caused by the accumulation of these errors. But the cause can vary a lot. Most of the time is because of the ambient, this is (people will kill me for saying this), the human could be considered a as a "pseudoinmortal" (yes, as crazy as it sounds) system if it is in the perfect ambient. This means: if the ambient has NO nocive elements, then the human can live as long as it's biology lets him to. Which, to this day, nobody knows, but surely is far more than 80 years average.

Nowadays, we live in an agressive enviroment with multiple factors which accelerate the aging process. One of them is the exposure to certain compounds, which interfere with the normal chemical reactions that occur in our cells (from the ones about cell division, to even other programs). This makes those "errors" accumulate, until it's impossible for the system to sustain itself.

Other factors are exposure to radiation (remember the ozone layer?, what about the contamination resulting from radiactive weaponry?), excessive stress (if the acute stress syndrome is too frequent, a human can enter in a permanent-stress state, which gives place to certain illnesses which compromise the effectivity of certain sistems, thus making aging go faster), genetic diseases (not much to explain here), etc...

So yeah, you are right in that sense. But our metabolism itself, is responsible for such little factors of aging, that basically it can be considered as not correlative to aging.

As you've seen, there are a lot of other factors which are involved more heavily in aging. And more responsible for it.

To clarify, I am not a native english speaker, so sorry if the medical terms are not accurate, but I hope the message is clear enough.

Edit: oh, i forgot about other living systems, for example bacteria, remember antibiotic resistance? That is also correlative to those errors, as parasytic systems also (vaguely speaking) leave a local mess, after they've been erradicated (which can take longer if it resists to a certain point the antibiotic), unless we already have antibodies for them.