At the start of the show, Jadzia was 28, not a typical age for a freshly minted officer. She was also a full lieutenant, which is also atypical for a freshly minted officer. I think the idea was that Jadzia was not a new officer, but one with some experience before being posted to the station. Which would mean she was not a particularly fast rising officer. Faster than most, maybe, but not incredibly so.
And Geordi graduated in 2357 with Riker, but was a junior lieutenant at least by 2362, and probably before that. Then he made full lieutenant in 2365 and lieutenant commander in 2366, which makes him a pretty fast riser.