Emperor Angel changing from Juv. to adult

I got one that is starting to show the yellow color and horizontal lines.
Question: It seems to me that it's way more aggressive now than ever before, starting to chase other tank mates around but get along well with my Powder Blue Tang. Is it normal for the aggressiveness? or is it just a phase?
It is about 3.5 inches long and 2.5-3.0 tall. The blue color is striking with different tones when seen at night (minimum lighting).
Thanks
 
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