...Even better, we had those three ranks for the CO of the same class of vessel: Kirk wore Ramart's braid while commanding the Enterprise to where no man had gone before.
But what's also interesting is the apparent ages, as Commodores could be more or less Shatner's age, while Captains could look older than Shatner. The very least we can say, then, is that even back in TOS, Starfleet didn't have an up-or-out policy strictly enforced at the starship CO level of ranks.
Dunno about "generally accepted": there's no onscreen suggestion that Picard would have become a CO or a Captain at a remarkably early age (indeed, in "Conspiracy" he seems to bestow this honor on one of his co-conspirators instead). As he reputedly took charge when the real CO was down for the count, he no doubt was called "Captain, Sir!" by his fellow officers at least once before the real CO came to (or was replaced by somebody less dead). But we have little reason to think that this would have lasted.
Friedman's novels just take the simplest route and parrot the vague TNG writers' bible suggestion, without canon backing. But if Picard made good at 28, and wasn't yet living the "Tapestry" reality, why did he then stagnate to the skipper of the irrelevant old tub for all those decades? What would have happened to his ambition?
Well, okay, it went away at some point, supposedly, because he has lost it by the time the "Tapestry" chance to relive it all comes along. Sorta. Kinda. It's an oversimplification of what "Tapestry" really is telling us. But something still turned this skipper of a rust bucket into the CO of the UFP Flagship, with a promotion to flag rank awaiting just behind the corner. It's difficult to believe in such a rush forward if the past twenty years were spent in stasis.
Timo Saloniemi