In a flat organization, your boss is going to be irrelevant. I would gauge a company by whether the interviewers teach or belittle. I personally find belittling okay, and can learn in that environment. "fuck you, if you are such an expert, then you can explain it to me. If you can't explain it, then you are probably full of shit." I have no problem saying that, but most people won't/shouldn't.

I get high from learning no matter whether the people are assholes or teachers. Most people need good mentors that are not managers. Any organization where managers have time to teach are too hierarchical.

A manager can be a mentor regardless of the type of organization. What is important if you want to improve a particular skill set is that the people that are managing you truly understand what it takes to do your job well and can provide feedback on what you are not doing well from a "do-ers" perspective - more of an apprenticeship model.

I have personally found that mentors are great for career advice and resolving questions, but never have enough "skin in the game" to invest their time in my development.

I used the word mentor incorrectly. What you want is peer teachers, not mentors. Mentors by the corporate definition are largely useless. You contact them 1-2 per month at best, which is pointless.

What you want is a person that observes your code, behavior, interactions, demeanor, etc., and tells you how to do better. It is impossible to have perfect introspection. You need to find a guide more than the corporate definition of "mentor". People need apprentice masters more than mentors, I wish I had used a better term.

that's pretty much what I meant... if you've just graduated that person is not really your 'peer', maybe not your 'boss' either ... a lot of times real world roles and relationships don't line up with org charts.

interesting... After about 3 years I agree. But a first job, someone's got to show you the ropes and get you up to speed with processes, testing, coding standards, help you get unstuck from time to time. I guess by boss I don't necessarily mean team manager, but whoever that is, mentor, direct senior. If nobody has that role, you'd better be pretty self-directed. 'Flat' better not be a synonym for free-for-all with no process, standards, code review, or you might learn some bad habits if you're not a natural (and even then.)

Most important thing in your first job is that the team is well balanced. And that you are collaborating with people who are amazing, rich and had history of doing great things before. [As to your boss, of course having a nightmarish boss fresh from some traditional caste system could be disastrous and can end up haunting you. But that's an outlier case.]