The way I have it in mind, the amount of chemical one is exposed to doesn't always accelerate their growth. Instead, there is "potential" growth. The more chemical, the more potential - to a certain degree. Too much, and the results are abominable; you'll find that out later. In any case, even if he was exposed to more, I would still say Ava developed slightly faster. Zayne has a higher potential, however. Not to mention, despite growth, potential and development speeds, no single trait will outweigh training and experience. For instance, the "strongest" character right now is likely Lily, an actual ghost girl, followed by Penelope. Penelope seems to have an average amount of exposure, and is even younger than Zayne. The difference is, she is part of the Masters facilities and then embraced the change.
So, all in all, I'm not really concerned with how anyone here... interprets their powers as much as offering a better plot device that can be justified. I believe it would be better for Ava to have played around and even understand some of her powers while Zayne is timid and rejects them, so that the plot mechanic of exploring the Spectre powers can be one of mutual bonding and trust.
I should say there will never be a point in this roleplay where any of these main characters are going to be able to say, "I had more exposure to the chemicals at first, so my powers are stronger!"
Now, if they were exposed to more later, experimented on, or exposed in a different way that affects their absorption, then so be it. But, these initial amounts and their age won't matter that much. Use them for plot devices.
