I think the concept of a character as young as ~30 being the head of the KPR is fine, as long as you roleplay out a decent explanation as to why that's happening in the first place. A recently fought civil war and the removal of more veteran police officers that may have sided one way or the other is at least reasonable if you play it out with that in mind. In fact the idea that the KPR is mostly made up of formerly junior officers that were forced to step up into the shoes vacated by the veteran officers that were forced into retirement could be an interesting roleplay perspective.
As far as the reference image for your character, I personally don't find a major issue with it, but I can see how others would. Perhaps you could simply use a less stylized appearance for your character, while still keeping the same look. Using cosplays of a character from an anime is going to lead to a look that overly accentuates the already youthful appearance you're going for. Your actual RP, has from what I've seen of it, been well thought out and written, but it may be overly zealous, though that may simply be the character itself coming through properly. I think perceptions of other players from the past may be influencing reaction to your character as well, 13-year old catgirl admiral is a very old joke around here.
All in all, I'd just look at using a more neutral and/or less stylized picture for your character. I have to agree with Luna, in that I don't really care what someone's character looks like because that's secondary at best to actually playing the character, but other people get held up on that, and you may need to make a concession to avoid the issue in the future.