This is from Young Jeezy's music video, "All White Everything." The Mercedes logo and the model number have been removed.

I'm trying to figure out:

A) Is this an S550 or an S500?
B) Circa what year?

S500/S550 is just an engine difference... rather find first which model it is. If it is a S-Klasse of previous generation it is a W220, but I am not sure it is that rather than a R710 (SLK) or C215 (CL)... all had this kind of rear lights but none seems to match exactly

It's definitely a current S Class W221, with those kind of taillights and that painted chrome strip. 170 SLKs didnt have the crhome strip and slightly different tailights without painted inserts. CL C215s also had diferent styled tailights and had their own visible numberplate middle part.

By the way, there is no real difference between the S500 and S550. The model is called S550 in the US, Canada and Japan (according to Wikipedia) and S500 everywhere else. The engine is the same 5.5-liter unit in both the 500 and the 550.