Let Solomon stay in HS and get a HS degree and work to improve his English, if that is what he wants to do (especially if the HS officials for his county don’t care if he is age 20 or 21). But if he is over the HS age limit to compete in XC/track, then he must not be allowed to compete in HS races. Age rules for HS sports competition make a lot of sense for many reasons.
If Solomon can still meet the age requirements for competing in Footlocker or NOC (perhaps they only require one be in HS) then let him compete there. If not then he can run road races for the next two years while in HS, and compete in college/open track meets as a HS athlete. That is what Molly Huddle and Lindsay Sherf had to do when their crazy HS coaches wouldn't let them stay on the HS team. And that is what a lot of home schooled kids (e.g. Josh & Jordan McDougal) also successfully did. They all got better by competing in open meets like the Boston High Performance meets.
If Solomon can link up with a good private coach and run in open meets, that is probably better preparation for college running anyway. His PR track times will likely improve more with a good private coach, and college coaches are going to be more interested in his PR times than in what HS meets he won.
With widespread publicity about his age controversy, no college coach is going to touch Solomon if he insists his age is 18 -- unless he has solid evidence to back it up (appears unlikely) along with a believable story why he entered all those road races and signed an application stating he was age 20. The NCAA will likely demand better proof-of-age than will the state sport governing board for his HS. WARNING: If Solomon tries to use fraudulent documents to prove his age and gets caught, his college running opportunities will be over.
My advice to Solomon would be to quit his HS team and stay in HS for 1-2 more years to improve his: English, education and running (under a good private coach, most of whom would coach him for free).
If he can legitimately enter a HS in NY, another option might be to move to NY and train/live with all the elite Ethiopian runners running for the Westchester Track Club. He would feel at home with fellow Ethiopians, could share living expenses with them, have an excellent coach, and have easy access to numerous open races nearby. But first he must come clean about his age. A few years under a very good private coach might bring down Solomon’s times to where he could become a solid D-1 recruit.