1) In the first film Spike is a hatching so it is obvious why he is not speaking during that movie. In your personal head-canon does he still not speak due to the fact he is too young to do so, or do you think there is another reason for his lack of speech?
Belated response here. But I just watched "Through the Eyes of a Spiketail" yesterday and so I wanted to chime in with some new thoughts regarding this question. I was hoping that this particular episode might help better clarify things... but instead I feel more confused than before.
I speculated last time that Spike's lack of speech was due to him being too young and not fluent enough yet, but as he got older he'd be able to speak properly. But the TV episode shows that he
thinks in perfectly coherent thoughts. In itself, this would cause me to speculate that either Spike has a physical inability to speak properly despite still thinking intelligently, or else he simply chooses to remain silent for whatever reason.
... ...
except that the episode also shows that he apparently can't understand his friends' words. From his POV shots, he hears the rest of the Gang speaking unintelligible garble. Now
this in itself would make me think that he speaks an altogether different language from everyone else. But then that theory doesn't really make sense because all the other spiketails can speak normally. And, as mentioned earlier, Spike himself has spoken the very occasional word in the same language as the others ("Ducky!" "Mother!"). So then why does he hear his friends speaking garble?
...
Yeah, I no longer have a clear answer to this question. Now I just get confused the more I think about it.