Like most jobs, it depends on the company. That having been said, so long as there's no nepotism, even a junior strategist is almost certainly going to be a very senior person in the company with many years of experiences. It's my impression that only VBCs have a position that could be considered a junior strategist. (At least, excluding companies like one I've interacted with who hired the CEO's son as a junior strategist until it became clear that wasn't a good fit - but they made that position for him, and it went away when he changed roles.)
Everybody I've known who had a strategist type job (apart from the CEO's son mentioned above, of course) was a recognized master of many disciplines, most of them being within one domain, but also including at least one of providing corporate training, giving technical presentations, or giving executive presentations. I know of one company that also allows for trade journal publications and published books that made it to recommended reading lists for the subject to count for the 'at least one of' list, but I don't know of any of their strategists actually qualifying on the basis of either of those.