Is there such thing as a 'runt of the litter' w/ringnecks?

[enigma9888]

After losing my 6 week old lutino ringneck to kaytee hand feeding formula, my breeder gave me 2 more ringnecks- a green and a blue. They were babies (roughly 3/4 weeks old)....but approximately 1 week apart (according to my breeder); the "older" one was obviously larger. Now both ringnecks are about 2 months old. The younger ringneck is SIGNIFICANTLY larger than the "older" one. Is this normal? I was wondering if there was such thing as the 'runt of the litter'..... Both ringnecks are still hand-fed, and eat seeds/veggies, however the "older" one eats very slowly, eats less formula, but still eats, nonetheless. I also noticed that it is more aggressive, bites, and only wants to be on our shoulders, whereas the younger one is more social and less aggressive. Is this normal? I guess I'm just paranoid after losing my lutino.....