So a Tradeline apprentice would probably be classed as 'cadet' in RL military but it is much more like old-fashioned Age of Sail midshipman starting your career as a teenager and learning on the job
A 'half-year lieutenant' is outranked by a 'four-year lieutenant' but that's a pure seniority thing, an outsider couldn't tell. (Obsessive careerists like Tayrey don't want to take breaks because they will 'lose seniority' relative to people who don't)
The next step up is to manage to get yourself working with a captain who owns multiple ships. You then might be given one of these ships to fly because said captain can't be everywhere at once. Which makes you 'lieutenant in command' - hovering somewhere around RL lieutenant commander/commander, got responsibility but not a captain.
It's situational though, if you lose that ship somehow you're back to lieutenant of however many standard years. But when you have a little ship you're not following the captain around in a mini fleet, you're operating independently, taking your own contracts.
You can ask the captain for advice, if you're close enough for the message to get there, and the captain gets a nice percentage of your profit-share, but that's it.
And then to be captain you have to buy your own ship and once you've got it the seniority counting starts again, although colloquially 'senior captain' means someone with multiple ships and/or has been captaining a long time.