If I recall correctly, the Edenians have a big lifespan, not all outworlders. Subzeroes are indeed descendants of the outworld, but you can see Kuai Liang significantly aged in MK Deadly alliance, while in mk2 is around 30… So it seems he ages normally, unless the dragon medallion which later acquires, grants him youth or something.
There's really no data to suggest how old the cryomancers live or how they died out, but given there aren't really any around in Earth except the two Subs and Frost (and even they are probably hybrid children) its a safe assumption they die normally. The only confirmed outworld natives are:
Shao Kahn is said to be "ages" old, but worked for Onaga who was sealed away at least a millenia ago and ruled for milennia.
Bo Rai Cho is another outworld native, who seems pretty old and only has about 200 years of history on him.
Li Mei is another outworld native, seems pretty young but its not said.
Reiko (possibly an outworld native) fought in Shinnok's first war against the elder gods which is also stated as pretty long ago.
The other kinda outworld natives are:
The Saurians (reptiles people) seem like they age pretty slow, but they are originally from Earth so maybe not.
The Tarkatan are said to be either half netherrealmian or at least originally netherrealmian, but they don't know who Onaga is so they can't have been around that long. Ashrah, (another Netherrealm native) is said to be "ages" old though so its unknown how long netherrealm natives live either..
The Moroi (vampires) seem to live obnoxiously long, but its not said how long ago their realm was merged, only known that Shao Kahn did it, which means they haven't been in Outworld as long as Onaga. She also doesn't seem to know (or care) about the Dragon King so she can't be that old.
I don't understand why the internet has a boner for "bad guys". Why you want a "bad"subzero? one angry puppet Scorpion is not enough? Bi- Han as a ruthless assassin who is a minion to the grandmaster's plans and later becoming a hell's wrath is not enough?
Kuai Liang started as an assassin for the Lin Kuei anyway.Then later committed on becoming Raiden's trusted warrior, while working to make the lin kuei clan a force of good,but always workin'in the shadows. That's a great archetype for an anti-hero, much more interesting than anything around revenge, anger, or becoming the world's best bad guy. fuck
I wouldn't like a third brother or whatever lin kuei as Sub-zero. seems cheap. Kuai is one of the most developed characters in terms of personality , and i would like to keep it that way.
In my opinion (and most) the rivalry between the two of them requires Sub Zero to be a villain. The second you make one of them a hero the other becomes the villain and you turn the rivalry into righteousness, its why both of their plots spun completely out of control by Deception. The problem is Scorpion is a complete one trick pony, if you take Sub Zero away, he has nothing which some might be okay with, but NRS put him on the damned logo, so there you go, evil Sub Zero lives.