Author's Note: Sgt Frog/Keroro Gunso doesn't belong to me (obviously) and everything belongs to their original creators. Also, kudos to naxin21 for helping! I couldn't have done it without her!
Alright, I'll skip to my point: I have a vague idea of the platoon's ages. Please note this is just a little headcanon/theory, but here are the ages:
Giroro-20Keroro-20Dororo-20Kululu/Kururu-18Tamama-16Let's start with episode 8, where Kululu was introduced, and he shot both Aki and Giroro. Kululu mentioned it shaved 20 years off your current age. When Giroro was shot, he turned into a baby. That's how I came to the conclusion that he was roughly twenty years old.
Then, in episode 24, the platoon and Hinata siblings were filling out complaint forms, and Giroro (he helped a lot in my theory) asked, "Do you want our age in Keronian years or Pekopon years?" Meaning that there are two different timelines. Keeping in mind Keron's immense humidity, it's safe to say Keron has at least a two-year differ