I recently took jazz (tag) in to get his nails trimmed and such and asked them to weigh him. He weighs one gram less than when he was at 4 months old. He is 16 months old now. The vet was out so i was not able to ask him if this sounded right. He weighs 263 grams. He is an absolute difficult eater when it comes too fresh fruits and veges but i am able to feed him the ground harrison mash with oatmeal twice a day. Does this sound right...should he weigh more than he did at 4 months of age? I know at that age he looked fully grown although people remark about how much bigger he has gotten although i do not see it.

Possibly 263g is a little on the low side for a tag, but they do come in different shapes. Also since I am not familiar with tag I may be wrong. Being under or over weight is sometimes more about the birds body condition especially around the keel bone than the actual grams on the scale. Also keep in mind that to get an accurate weight, the bird needs to be weighed on the same scale at the same time of day. Birds are always heavy and full late in the afternoon just before bed time. The variance in one day can be 10%.
The best time to weigh a bird is after the morning poop before breakfast and this way you know you are only weighing bird and not anything else. Did the technician think Jazz was under weight as the technician should be a bit experienced with feeling a birdie condition?

Tags should weigh between 275-400 grams.
I wouldn't worry about his weight being a little low.
Is his length proportioned to his weight?

Ruby's weight goes down a bit when she molts. Is he molting? Wish I would molt! ha!

He still seems to be molting but not as many fluffy feathers at the bottom of his sleep cage so maybe it's over

Does he fly? Flying birds often weigh a bit less than ones that are clipped.

No he has not flown that much. His wings had not been clipped for 8 months but he does alot of walking up and down the steps