Man her old manestyle from Season 5 makes her look like a middle aged mare. I used to think Statlight was like 40. But seeing the rest of the episodes especially since she has a middle aged mother, I personally think she is in same age range as the Mane Six, perhaps she’s 23.
I bet that was intentional. Dictator Starlight wanted to look older and more mature than she really was.
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To boost her ego about being wise all knowing ruler.
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To make the other villagers of Our Town think of her as wise capable mother figure who would have the skill and maturity to lead them to harmony.
But in reality Starlight was not as mature as she let on. She was still a confused lost young mare who tried to act more mature than she really was. That kind of shows how immature she really was in that way.
Once Starlight was reformed though, she wanted to look more like an average young mare. A friend not a distant mother figure. And only then was she able to learn true maturity.
Well that’s my headcanon/essay of Statlight Glimmer. Personally I like her with her new mane more. It feels more casual and friendly not distant and authoritarian.