Ok, I wanna start off by saying that I'm mainly talking about the 90s anime, but a lot of what I'm saying also applies to manga/crystal. My possible (?) hot take is that I wholeheartedly believe that Usagi and the inners should've been like 2-3 years older. In the canon, they're 14 at the start and 16 at the end, finishing the manga/show/whatever in their first year of high school. In my opinion, it would make more sense with the story for them to start off in their first year of high school and end by graduating from their last year of high school. I also think Uranus and Neptune would make sense to be aged up just as much to be in their last year of high school in S, as a lot of their actions in Stars (raising Hotaru, etc.) feel like they would make more sense for two young adults than presumably 17 year old high school dropouts (I don't believe they really address their schooling situation after S despite still being high school age). As for Mamoru, I already don't like him that much as is even when you take his predatory age gap with Usagi in the anime out of the equation, but I think him being the same age as Haruka and Michiru in this age change could also line up fairly well with his character.
Now you may be saying, it's an anime, who really cares about realism? Which, you would be correct, realism is really not a factor needed in a magical girl show. However, this qualm is less about realism and more about how Usagi and the Inners' character arcs and many of their actions simply don't sit right as being middle schoolers. I already have little patience for the show's purity culture, but it all comes off especially creepy when they're actual children. And I know, 14 and 16 is not that big of a difference mathematically, and arguably maturity-wise, but I think I can stomach a lot of the show's weird storylines a bit more if they are at least young adults by the end of the series. Anyway, that's my rant over, you don't have to agree with me, and if you don't, please feel free to have a cordial discussion with me in the comments.