Voltron Paladins’ ages stated in the Book
I am pretty shure that they had those ages when it all began. We don’t know what time of a year it was. But I think at least it wasn’t summer, because it happened in the middle of school year. Let’s begin with November to December. All of them had had their birthdays at that point in the year and their ages were 18 for Keith, 17 for both Hunk and Lance, 15 for Pidge and 25 for Shiro (as it was said in the book). And when they were already somewhere in the Space, first Hunk turned 18 (when on Earth was January), then Shiro turned 26 (Feb), then Pidge turned 16 (Apr), then, after a while, Lance turned 18 (in July), and Keith turned 19, three month later (Oct). We will return to this period (Nov-Dec) later. Now let’s try other options.
If it was in January-February (after Hunk’s birthday when he turned 17, as it was his stated age in book, and we decided that that was their ages in the beginning of the things), then Hunk stayed 17 for the rest of that year, when Shiro turned 26, Pidge - 16, Lance - 18 and Keith -19. In that case Hunk was 16 in the beginning of the school year, Keith and Lance - both 17, Pidge - 15.
If it was in March (after Shiro’s and Hunk’s birthdays), then Hunk stayed 17 and Shiro stayed 25 for the rest of the year, when Pidge turned 16, Lance turned 18, Keith -19. In the beginning of the school year younger paladins were the same as it was said in the previous paragraph.
If it was April-May (after Hunk’s, Shiro’s and Pidge’s birthdays), then Hunk stayed 17, Shiro stayed 25 and Pidge stayed 15 for the rest of the year, when Lance turned 18 and Keith turned 19. In that case Hunk was 16 when the school year began, Pidge - 14, Keith and Lance - both 17.
If it was in the summer (unlikely, as I’ve said earlier), before Lance’s birthday, in June-July, then the situation is the same as was depicted right above.
If it was after Lance’s birthday, but before Keith’s, in August-October, then Lance and Hunk stayed both 17, Pidge -15 and Shiro - 25 for the rest of the year, when Keith turned 19. In that case Hunk and Lance was both 17 when the school year began, Pidge - 15, Keith - 18.
I personally think that it was November when it all began (my first option). It’s just more likely to be this way, judging their ages in the beginning of the school year: Hunk, Lance, Keith - 17, Pidge - 15 (because she’s a genius). At that point, I repeat, they all had had their birthdays in that year and at that moment had ages stated in the book. Therefor, in my opinion, their birthday dates look like that:
Shiro - Feb 29, a leap year. Let’s take that year as a reference-starting point, as a zero, for our purposes.
Keith - Oct 23, a 7th year after Shiro’s birth.
Hunk - Jan 13, a 8th year after Shiro’s birth .
Lance - Jul 28, a 8th year after Shiro’s birth.
Pidge - Apr 3, a 10th year after Shiro’s birth.
I started to think of all that stuff because of this post. Thanks @irrevocably-delicious for inspiration!