This is a description that I found:
"The CAG and TAG as a baby parrots will have dark grey to black eyes up until they are roughly 6 months of age when their eye color starts to lighten. By the time they reach a year, their eyes become a pale grey color. At about 1.5 to 2 yrs their eyes will turn a pale straw color. And lastly at about 3-4 years of age, they will have a light yellow iris. This is one way to be able to determine an estimate of how old a baby is when visiting bird stores. Grey's usually reach maturity at about 4-5 years of age."