There are a ton of factors that are taken into account when you try to get an S.
Unfortunately jungle is a bit harder to get an S because it's hard to rack up cs.
-
How long was the game? If it was really long then 165 cs could be too little
-
You have no assists
-
Were you present during objectives? This is very important because the game tracks where you are. So if you want an S make sure to be there for as many dragons/towers/inhibs or whatever objectives that you can
-
Did you place a lot of wards? The game also takes into account how many wards you place
If that was a 15min game then I'd probably consider that to be an S. But at 20mins+, 7-0-0 with 165cs won't cut it especially because Kha Zix is a popular carry Jungler. So you're going to compete with players that usually go 15-2-6 on him or something along those lines.
An easy way to get an S is to take your champion into an unconventional role. E.g. I took Wu support 3 games and got an S back to back to back. I dunno about Kha Zix support, but it's worth a try lol