If someone was an average high school wrestler they should be on a blue belt level within months of starting in my opinion. They should have good hips and positional awareness and from there its just a matter of learning some submissions and technique from guard. But you get out what you put in.
The best way to asses where you are at skill wise is to compete. If your taking gold at all the comps its probably ok for you to jump to the next division.
Ok, yeah that makes sense then. Being a Martial Art, character traits like respect, and humility are equally important as whether a student can “beat someone up”. You are teaching people skills that can potentially maim if not kill other human beings (and were originally designed to do just that), so if you don’t also foster the development of a positive character and moral compass, all you are doing is creating “Frankenstein monsters”; which is the antithesis of the goal of Martial Arts.
This is actually one of the stark contrasts that I see between Martial Arts and sports like Wrestling, boxing, Muay Thai, MMA, etc…
Yes, there are individual coaches/gyms in those sports that stress character development; but as a sport/whole they tend to care more about who can beat who up and even reject things like the concept of implied respect for all other people (unless those people prove themselves unworthy of said respect) and instead operate on the idea that respect must be earned (usually by physical domination but sometimes by a show of mental toughness).
That’s not to say that everyone will gravitate towards Martial Arts and there are definitely sport based people that are supremely skilled. Just trying to explain, from my experience and understanding, why a Martial Arts instructor might choose not to promote someone who may have plenty of skill to deserve that rank, but be severely lacking in the character traits expected of that rank.
I explained the situation and told him I’d be wearing a white belt out of respect for the art of BJJ. Honestly, I don’t think he processed that information because at the time all BJJers were watching Sherdog videos with BJJ blue belts submitting alleged judokas and he didn’t think it was such a big deal.
Roughly after two months I got my BJJ blue belt. Once I familiarized myself with somewhat smoother transitions and held my own against purples and even browns there wasn’t anything I didn’t have covered. I could almost always fight higher belts to a standstill but my offense was lacking, despite being a judoka focused on my ground game.
Yep, that happens. People have no idea what hit them 
Judokas suffer from judo-specific rules when it comes to rolling, but once they overcome their ingrained reaction to turtle up when in trouble and realize that they have to advance from holds into chokes and submissions they can be formidable opponents.
But like with everything, it always comes down to the individuals or his school.