<adolescent mentality 即係點解呢?>
I am pretty sure you know what "mentality" means...you just wanna get a clearer understanding of what i am trying to say...so i looked up yahoo 字典:

- adolescent = 1. 青春期的 2. 青少年的;幼稚的,未成熟的
- mentality = 心理狀態,心性

i am not too sure if i had it translated correctly in the first place with "adolescent mentality", but as i went through a few Chinese online reviews about this anime, i think this is the right phrase i had in mind "年輕的少女情懷".

少男少女的情懷

I see.  Thanks for looking up.  

btw, the cantonese dubbed by female artist "janice" is not the right voice for the heroine of the story, it misses out the whole vibe of her tomboyish personality, not to mention Janice's English accent...