I did not read the book, so I wonder ow similar/different it is – in story, ambience, etc- More of "inspired by", "based on" or - how novel! - faithful adaptation?
Apart from the quality (as was already said, the young school-boy-looking-actors are usually not even actors), is it not similar to actresses - i.e. simple stereotypes about what is inn an alluring? If you are famous (which can - but does not always has to - mean good), you can/want only play the main lead. If you are main lead, you cannot be old (which in dramaland often means above 25 maybe a bit more for men), because being "old" is the ultimate failure and not attractive enough in this industry. It is more drastic with female actors - avenueX has a nice video about this - but even male ones are not completely free from this juvenile trend. Personally, I think it is a shame. The range of characters and consequently storylines is greatly reduced if your hero can only be a young vigorous youth trying to accomplish his dreams. It gets quite repetitive for the audience and I bet it has to be quite boring for the actors too.
Lmfao a strong female lead as Zanilia Zhao, she doesn't have the face for it.
She is an actress - it is not about having such and such face but being able to portrait a given role (normally appearance and personality can differ quite a lot). I would recommend watching story of minglan, you can see that she uses this discrepancy between looking young and naive and being opposite to create very interesting, and complex (in some scenes not far from scary) experience for the viewer.
Personally, I think it is a shame. The range of characters and consequently storylines is greatly reduced if your hero can only be a young vigorous youth trying to accomplish his dreams. It gets quite repetitive for the audience and I bet it has to be quite boring for the actors too.