system
Given the following post, respond as if you're commenting on Reddit:
human
[MHA] Why is All For One so damaged in the present day?

All Might said there were quirks that halt aging, and thanks to Recovery Girl we know healing factor quirks exist. So why didn't All for One just steal a healing factor and an agelessness quirk?
gpt
Most healing quirks like Recovery Girls don't actually fix the wounds. They just rapidly increase the rate at which the body heals, which is why Deku can't keep breaking his arms. They don't get reset to perfect, they just are naturally healing at a sped up rate. With the damage to both All Might and AfO after that fight, it's frankly a miracle either of them are still alive, let alone walking around. All Might lost most of his digestive tract for gods sake. AfO was durable enough to survive, but with severe injuries. Over time he healed up naturally, but the damage was so extensive he wouldn't ever be the same without a regeneration quirk. However he didn't discover the regeneration quirk used in the USJ Nomu until he was mostly healed, so regeneration would only restore him at best to the point he was when he first acquired the quirk. They touch on this a bit when first introducing AfO in the anime and manga.

The short answer is such a quirk wasn't found until it's use was inconsequential for his major injuries. The nature of the other quirks in his toolbox, especially the agelessness quirk, can only be guessed at for now, as no one but him know what they do at this point.