Edit: after some googling I found this result
> age 15 or 16 would be about the average age for bones to stop growing, so from that point on, there is no collagen regeneration in the cartilage. Your body, on its own, cannot regenerate the cartilage it loses in its adult years.
Blood supply does have a lot to do with healing-or-not -- taking the meniscus as an example, about 30% of the meniscus has a blood supply, the rest does not, so that if the injured part is of that 30%, it can actually heal, whereas if not, they can only clean it up and stitch it together like a rag doll ---
[for the curious : I got lucky and my injury healed tolerably well on its own sans surgery]
The cartilage in your nose and ear are different, and besides, the stuff that's blocking your boxer friend's nose, and causing cauliflower ear is not really cartilage. It's fibrous growth which has a blood supply. It's your body trying to replace real cartilage with a poor substitute.