Ive slays wondered why ansem SoD looked different. I mean where does he get his body from? I read on some thread that his clothes/appearance resembles young xehanort from behind, so is that what xehanort looked like when he was younger?

He would very much resemble young Xehanort

Ansem SoD got his body from possessing Riku(as shown in the game). We have never seen Xehanort's face when he was young(as shown in BBS). Until we see his face, we can only assume things(but it's clearly obvious that Ansem was based off Xehanort).

Well, his clothes are basically the same that Xehanort wore. I always thought Xemnas and Ansem looked more or less the same, but Ansem's look is more warped by the darkness because he's a heartless. So I guess that would be the reason for whatever diferences.

he is looking like young xehanort except young X got spikier hair.