That's not a racial thing as much as it is an individual thing. Not all individuals are the same. I speak in generalities, because there are trends. Bigger usually means more capacity. This does not equate to moral worth, intellectual capacity, or any other such thing. You can just hold more raw anima (because you have to to keep your body together). Dinosaurs are big and strong, but that doesn't make them better. Goblins are small, but that doesn't make them worse. Just different.
And the capacity needed for spell-casting, to be precise, isn't about raw power. There are lots of very big, very powerful creatures who can't cast a cantrip. Even a tiny, weak fey being (such as a sprite) can cast spells, because the total energy involved is small. But those connections are intrinsic and take time to develop. Just like sexual maturity, a hatchling just doesn't (always barring exceptional cases here) have that potential developed yet. It's blocked behind the rest of the things that must happen to develop.
As for simulacrums--the nature of a simulacrum is not as easy as simply quoting the rules. Because those are not the rules of the world. They're the game abstractions--things that are creatures (by the rules) are not necessarily ensouled beings (in the world) and vice versa. I'm leaving that one open and not deciding anything about it yet.
Not inherently. I know lots of kids (3-5 year olds) who can speak very well but have loose concepts of me vs not-me. More precisely, they don't really believe that others are real. A name, for a hatchling, is a label. Like a name for a human. As they grow, their names become them (and they become their names). To a post-hatchling dragon, their names define who they are and they are bound by their names. Hatchlings have arbitrary labels that mean me, but not NAMES.Someone who talked enough to learn 2 languages probably have a name and a significant identity.
That's possible, but that requires finding a high level caster. And those are rare. For example, in all the main play area nations, there are maybe 1-2 people who can cast 9th level spells. One's a cleric, one's a wizard. And he doesn't care about such things (being old and senile). He doesn't even know True Polymorph.Or you could convince a high caster to protect you from the problems of not molting such as asking a wizard to turn you into a younger hatchling(since you do not want to be turned into an older dragon since it creates tons of problems you mentioned) or even into an entirely different specie altogether. so trying to get to be a friend of one of those high level wizards that just sits there alone in a tower studying magic could be an alternate way of surviving.
They can, but they usually don't. Again, I'm speaking of the general case--there are always exceptions. In fact, there's one particular green dragon who is beginning that process. He's also clinically insane (disassociated personality disorder) and was never part of draconic society. Exceptions always exist, but they're exceptional cases.
I don't think the current God of Magic would look favorably on that situation. First, people who can cast that are really rare to begin with. Like single digits on a continent. Second, that requires messing with a spark. And that runs the risk of dealing with the demonic if things go wrong. And that would be a bad thing.
The current Demon Prince of Black Magic (sort-of) would also not appreciate shenanigans of that order.
Plus the risk of a dispel magic...
As a DM I would say no to trying to change the potential of a person in that way.
The spell takes care of that. The current God of Magic (who sets exactly what the spells can do) looks badly on spells of mass-destruction and so the spells have safety valves built in.
And it's not that size sets capacity but that size sets minimum required capacity. You have to be able to handle X anima to have a body of size Y. Polymorph-type (or shrink) spells provide temporary extra capacity (in either direction) as a buffer.
In principle, yes. But liches tend to fight a bottomless hunger. So it's possible but not probable.
It's not so much that "once people fill up with anima, they die", it's like they're a balloon. Each one can hold a certain amount of air before it pops. But if you fill it too far, it starts to stretch. Pulling the air out of a balloon that was near its limit (past the elastic limit) is permanently deformed. It's a homeostasis in the short-term, but growing on the long scale. And since anima is associated with memory and skills, traumatically losing anima tends to leave people disoriented, amnesiac, or more prone to sickness or more vulnerable to lasting injury.
So in general, lots of what you suggest is possible. It could happen, but it's not the norm (or even widespread). You might have one or two hatchlings that have "escaped" the molt. But they'd be rare because the forces (both physical and social) are just that strong.