Not military but my understanding is:
Commissioned officer: starts at second lieutenant, can go all the way to lieutenant general, have to go to specialized school (like West Point) to be eligible. Receive their “commission”/assignment directly from president. As the other commenter mentioned, BG is fairly high up.
Each service can have slightly different names for certain positions. And yes they split CO positions into three types, company, field and general, BG is the lowest “general officer”. As to how, you could always ask, but some combination of seniority/achievements. He almost certainly serviced in combat in Afghanistan/iraq as a field officer given the timelines.
Non-commissioned officer: these people joined as rank and file, and got promoted to oversee/command people below them, but didn’t go to specialized school, and can’t rise above sergeant major. So you could have a guy with 20 years of experience commanded by a brand new second lieutenant.
Rank and file: privates and the like.
You don’t want that guy. What you want is attention, and he was the last person to give it to you, therefore you think you want him.
Just get dressed up and go to a bar, and you’ll find enough guys who will give you that, without the red flags.