Seriously, how many people would still be alive had batman just killed the Joker on day one, instead of letting him escape one of the flimsiest prisons in history.
I suppose it would be quite hard to harvest organs from Wolverine because he'd just keep healing during surgery. You'd probably need the flash to do it. Haha
Superman wasn't normal, even by Kryptonian standards. It was the sun in our solar system that gave him his powers. Everyone back at Krypton, with its red sun, was just like a normal human being. Even among other alien races, Superman is unique. Not to mention an endangered species, being one of few Kryptonians left alive.
stress or just becoming a teenager. It'll eventually happen through puberty without stress, but stress just makes it appear faster (usually)
Also, something extremely tragic can trigger the mutation before puberty.
grimreaper is correct - if he was circumcised it wouldn't have healed years later as he grew and his mutant genes kicked into effect, it would still have the same scar tissue. now, if you cut the scar tissue or in theory the entire anatomical part it should grow back.
(So, using a different body part, if he had his earlobe pierced or cut as a child, and his mutant ability kicked in, he would retain the piercing/cut scar, he slices or burns that scar tissue away the earlobe should heal back completely, he gets his ear cut off it should grow back completely, but not until that style of action happens would anything change to the scarred ear).
The only drawback is how necessary he is.
Also, something extremely tragic can trigger the mutation before puberty.
(So, using a different body part, if he had his earlobe pierced or cut as a child, and his mutant ability kicked in, he would retain the piercing/cut scar, he slices or burns that scar tissue away the earlobe should heal back completely, he gets his ear cut off it should grow back completely, but not until that style of action happens would anything change to the scarred ear).