welcome to the forum and congrats on your new little rescue. he/she is gorgeous.
i agree with you about 6 months plus. the bars on his head may STAY the way they are now. it is the bars that would have been down the FRONT of the head that would determine a younger age along with the eyes.
can you see the lighter color around the outer edge of his eye balls? that will also help determine age, as stated above.
is there a tag on the leg? that will tell a YEAR on it so you could even go from there for age.
i had the same problem you are having when i found Sky. she was older and i figured her to be around 9 months when i found her. it is hard to tell the sex and age in quite a few keets, unless taken to an Avian Vet for confirmation.
just so you know, i have 2 FEMALES. that is determined by there ceres being WHITE around the nose holes and pale blue on the rest of the cere.
good luck figuring out your new bundle.