If Goto joined the police forces at 18, then he most likely joined without being a college graduate. That would limit the types of positions he could hold and would keep him out of the more elite Japanese police forces. He also would've had to spend a year in training.
It makes more sense for Goto's character as we know him thus far if he joined as a college graduate and was in one of the elite police squads, like a riot cop or Imperial Guard. College graduates only have to train for six months and can apply for more important positions.
The only way Goto's backstory makes sense as it stands is if he turns out to be some kind of police work prodigy. Then you could say he did elite work despite skipping college or just graduated from college very young. That feels a lot more labored to me than just pushing Goto into his mid-to-late 20s, though.
Terui kinda had a similar problem in W, though.
We're just flat-out told that Terui is a prodigy when they introduce him, which-- in pulpy Japanese writing, anyway-- always explains away really young characters having positions of authority. Terui is a pretty exaggerated guy from the start so I felt he worked well enough.
Goto is presented as more of a gritty and down-to-earth character, which... would, honestly, only be enhanced if the character felt a bit older. I'm not sure you can really get away with a gritty and down-to-earth youth police work prodigy. Well, I'm not sure
OOO can get away with that, anyway.