That age is wrong. Asami is a high school student. Going by the ages the other characters have in the beginning of the show (Fuyuki in the beginning is 12 and at first year of junior high, Natsumi is 13 at the second year), Asami would be likely 15, 14 at the youngest. By the last season, Asami is even making university entrance exams. Mois doesn't look any younger in her true form compared to her Asami form so she seems to be around the same age too.
But, yeah, either way, there's a big age gap.
Nope, official translations died alongside TokyoPop. There are fan translations, but they're pretty hard to find, and not up to date.
oooooo! how was Tamama's image of Keroro destroyed? does the same thing happen to Mois?
Nah, just Tamama. It's a scene in vol17 during a meeting where he's shown to be bored and then starts thinking about how Keroro is just another boring old adult whos talks meaningless stuff and that the childhood stories that he heard about Keroro "back then" were likely just urban legends. Keroro then asks him if there's something wrong, but Tamama just smiles and says that it's nothing. Even the relationship chart in the beginning of the volumes changes at this point, with Tamama to Keroro being listed as "Reverence?" From this point on I don't think he ever fought with Mois either in the manga.
The anime delayed animating that chapter until the last year(which included some chapters even from vol 21), and even then just treated it as a one episode thing and he was back to normal the next week. The anime even added some scenes where he's jealous of Mois in adaptations of manga stories from after that point, where that didn't originally happen.
Yeah, Tamama outright says he wants a "dangerous romance" with Keroro in the manga, and although that line was cut from the anime it's still pretty obvious that he has a romantic interest in him - there's an entire story about him wanting to kiss Keroro (266) and he also attempted to do it in an episode where he switched bodies with Fuyuki (316). He's a childish teenager not an actual child. Note that he's just as tall as the adult Keronians, while when Keroro and Giroro are turned into children, they're smaller than Tamama.
Ironically, later on in the manga Tamama's image of Keroro is destroyed and that also seems to kill his crush, but the anime delayed adapting that and even when they did do it, just ignored that scene and kept it even in later stories (it's that bit in the beginning of the Zoruru vs Dororo rematch episode).
In the early anime episodes, Keroro's childhood seems to take place in the early 80s, right after the Gundam boon. That's basically retconned away later though since it doesn't actually make much sense with some other elements of the series - like the aliens actually being much older than humans.
In later anime episodes, Keroro's childhood is generally depicted as similar to middle 70s Japan (so the same would go to Giroro and Dororo) based on various toys he's shown playing with, like thinly disguised versions of Atlanger and Gattai Yamato. Attempting to give actual dates to them doesn't really work though, because the Keronians are actually much older than humans. Keroro is officially listed as 10500 years old, and although that's in Keronian years, rather than Earth ones, he's older than Mois who he met as a small child but was already teenage looking when she arrived on Earth 500 years before the series. So, even if Keronian years are shorter, by the time Keroro was a child Earth should be nowhere near modern age.
The anime did add a bunch of scenes of him teasing Giroro and even being annoyed when Giroro shows fondness for Natsumi a couple of times. It's anime-only though, and really started happening out of nowhere in the later seasons. And, obviously, they never actuall play out seriously, it was basically fanservice since a large part of the Japanese female fans seem to ship Giroro and Kururu.
As far as a return of the anime goes, I'd guess they'd do some kind of introductory story (a remake of the first chapters or something original) but then do some stories that Mine did relatively recent in the manga that randomly took place around the beginning of the series rather than adapt the other actual early material aagain. After that they could just go on and adapt later material that wasn't touched by the previous series.
If there's another set of gimmick episodes like KeroZero or MushaKero, I'd like to see something with the Kemono friends forms of the Keroro platoon.
Kururu is associated with India due to his curry obsession, but they've also made associations with Russia too (His appearance in the KeroZero short, also talking about "borscht" rather than curry." There was also a Kururu lookalike in Arcade Gamer Fubuki (maybe it was Kururu himself since he had a Keronian mouth, although his face was human colored) who had a Russian-like name.
All the others are pretty much Japan as far as the manga goes, like the childhood shots, toys and such. The anime gives some more variation, but even there Keroro and Tamama are pretty much just Japan. Tamama is often seen dressed in Japanese gi and such when training, and then there's the shounen action parody elements around him, like the energy blasts and SSJ transformation.
Giroro ends up associated with some American stuff in the anime though due to his VA dubbing movies and his general war interest, which brings up American war movies. However, then there's his hidden train obsession which is distinctively Japanese.
Dororo is actually kind of odd though. Although he's all Japanese style, the point is made that he's more like someone mimicking a Japanese, rather than an actual one, like how Koyuki makes fun of the accent he gains after spending some time in the ninja village, saying that it's like samurai from movies. His original name and the name of his original style "Assassin Magic" is all English too.
Hope, I don't think there's one. The character lists generally separate Keroro Land characters from the others though, and there aren't that many manga-only characters, especially if you count the flash anime episodes too.
Not counting the episodes where only Pururu appears...
Episodes 100-104
Episode 130-B
Episode 154
Episode 183 (Garuru-only)
Episode 245-A (silent cameo)
Episode 254-B (only Pururu and Garuru have actual roles, the others only make a silent cameo)
Episode 291-B (Garuru-only, and it's just a cameo)
Episode 296-A (The Keroro platoon receives postcards with messages from various characters, including the Garuru platoon)
Episode 336-A (Zoruru and Garuru-only)
Episode 344-A (Pururu-only, the others make a silent cameo)
Episode 356-A - The episode shown in that picture. Only Garuru and Pururu actually get voiced roles though. The others appear in a couple of scenes, but don't speak.
182-B too.
316-A is Momoka focused, but also heavily features Tamama, although that's a spoiler in a way...