SBS Volume 4 answer about Shanks WTF

In the first ever SBS there is this:

D: How old are Luffy, Zoro, Nami, and Shanks, respectively?

O: Ages, huh? This question came up a lot. Like, a whole lot. In terms of sheer volume, I bet this was the #1 question! Let's answer! Currently, Luffy is 17, Zoro is 19, and Nami is 18. As for Shanks, since I don't know where he is now, I'll give his age from 10 years ago. He was 27 when he was in Luffy's village. Oh, and Usopp is also 17, same as Luffy.

Why he asnwered: As for Shanks, since I don't know where he is now, I'll give his age from 10 years ago. Like it is a mistake in translation? Why does it matter where Shanks is to gives us his age. I dont get it.

Some people theorized that >!time runs differently on Elbaf!<, although I don't really believe it. I know it's total nonsense that there would be something connected to >!Elbaf !<and this theory in this SBS, but I really don't understand why it's important where Shanks is in order to give us his current age.