'Cause Shao Kahn rubbed his anti aging cream all over his face.

Shang Tsung's MK2 bio:



basically, this, and he has been aging ever since...I think.

The power of stealing souls is better then Clearisel, and Proactiv put together!

I thought he needed to steal souls to not only stay alive, but remain youthful.

That's correct. He ages faster than normal if he goes long enough without stealing any souls because the gods cursed him.

The reason Shang Tsung was old in MK1, and then shown to be younger in subsequent games, is because Shao Kahn restored his youth. The scene was depicted in the MKII comic (click to enlarge):



MKSM has conflicting information, considered non-canon. John Tobias's MKII comic is considered to be the authoritative source on what happened.

Awesome, thanks Kombat! I really wish I could get my hands on that comic book. I wish they made a series of official canonical (is that right?) comic books or graphic novels from MK1 through to Armageddon. Not just to clear things up, but I reckon it'd be entertaining as hell.

How many canon comic books did they make anyway? I know there wasnt any for DA onwards. Or was there?

As far as "official" comics, I believe only the John Tobias MK1 and MKII are considered official and canon. MK4 had a comic (not by Tobias) but some of the info contradicts the game. There was an MK vs. DC comic drawn by Tobias as well, but as the design team has said that's more of a "What if" scenario. MK Deception also had a comic, inked and written by WAM Entertainment, that came with the MKD controllers. It didn't go too deep into the story, so it didn't really contradict anything from the game.

and stated in Tsung's MKII Bio...

If I am to judge it by the story, MK1 Shang Tsung is a decrepit old man because he hadn't consummed a decent quantity of souls for a long time (a benefit which not only enables him to see through the battle techniques of his victims but also prevents him from aging and dying prematurely). Makes one wonder how come Shao Kahn had never thought of restoring his youth BEFORE Tsung fought Liu Kang in the first tournament.


Then again, aged or youthful, Shang's the only MK villain never feeling too powerless or reluctant to try and rock the shit out of the Earthrealm's champion.

Actually, it's just a prologue, nothing in it happens that contradicts the canon so it fits, but there's no meat to it either so it's not worth tracking down if you didn't buy the kollectors' edition of the game and get it.

All that happens in it is we see Dark Kahn being created and starting to make people feel "THE RAAAAAAGE" so they'll fight each other, then it shows brief glimpses of several of the fights in Story Mode, like Flash/Kano and Shang/Wonder Woman, with everybody's eyes glowing yellow.

The only interesting scene is a single panel that addresses the "disappearances" Liu and Kitana are talking about at the beginning of the game. When Dark Kahn starts reaching out with his powers to affect people, Johnny Cage, Goro, Aquaman, and Robin are shown being hit with yellow lightning and just plain erased, explaining why they're not in the game.
Also, the MK4 comic doesn't really contradict that much. It follows the pre-Deadly Alliance idea that Edenia and Outworld were just two different names for the same realm so it has Sindel ruling Kahn's old kingdom, and she banishes Reptile to the Cobalt Mines of Shokan instead of to the Netherealm, and Johnny Cage isn't brought back from the dead, he just shows up hanging out with Sonya like nothing ever happened, but other than that, it fits pretty well.
Besides, the MK2 comic had inconsistencies too, mainly the way Scorpion shows up at the end and seems to already know Subbie's different and made the vow of protection before the tournament even got started. And yet we consider that official.
I never knew the Deception comic got released, though. I thought it was just never finished. I'd love to get my hands on a copy.

because he chose....poorly

Question's been answered, so I'll lock this.