I was redirected here after a mix-up

But, while I was watching Mysterious Island the other day, the beginning struck me - when the Gang is watching the last tree star and are arguing over who should get it. Cera says, as she walks up to the tree. "I think it should go to, say, the oldest."
Littlefoot protests, "But that's you!"
Cera grins. "I know."
So that would Cera the oldest, and since Littlefoot confirmed it himself, it's further proof. Unless Cera just holds that above his head to jab at him

but another thing - we see Ducky hatching and everything, hopping along after the frog, but when it cuts to cera, we still see her in an egg, yet she is chasing her sisters! How would she know who they were without having been alive at least a little bit longer?
IDK, my chronology of the Gang falls as so: Cera, Ducky, Petrie, Littlefoot and Spike.