Re: iron stores - they don't 'run out' at 6 months. 6 months is the age they begin to deplete. They're fine on milk only for a lot longer than that and there is NO need to swap to follow on milk.
Ellie got bloods done at 20 weeks and her iron levels were virtually none so she had a blood transfusion, the doctors cant tell me whether it was cause they do get lower round 6 month, she was prem or us one of they things x
Iron stores deplete earlier in prem babies obviously because they had less time on the womb to build them up. So a baby born 3 months early could have depleting iron by 3 months iyswim, but I don't think it is an exact science x
https://kidshealth.org/parent/medical/heart/ida.html#
Prematurity and low birth weight are other factors that put an infant at risk for IDA. Before birth, full-term, normal-weight babies have developed iron stores that can last them 4 to 6 months. Because preemies don't spend as much time in the uterus getting nutrients from the mother's diet, their iron stores are not as great and are often depleted in just 2 months.