It is scary when you look at it in those terms, my SIL weaned my neice before she was term! She wasn't even as early as Tink
Latest studies have found that children don't need food in their first year, it doesn't have as much in it as milk does so there isn't the same rush anymore (theoretically in advice) to get solids into children or to replace the milk meals with solid meals. It is a shock I should imagine when you have older children and have been told the importance of solid food for years!
Don't think of Callum as being any age, just watch his developmental age, when he is behaving like a six month old, then think of him as six months. Age is a horrible thing with a premature baby, you end up having several "ages" to factor into things, real age, CGA, size, clothes size, developmental age...
WRT growth spurts, they will happen at the CGA, but you may also find him having them at his birth age too, so try to look at both ages when he goes through them before you decide if it is a hunger thing.
If it helps, Tink is 18 months old and I'm looking at all of this thinking "how do you remember all of this?" but I did, it becomes second nature as you go through it.