For a 15 year old royal, it's more " daring " than I would expect. Not for most just a conservative Belgium royal one.
Yup, the dress is very contemporary considering it's the BRF and mom Mathilde always dresses like she's 20 years older than she is.
Mathilde wears Natan which is worn by MT (who I believe is in her 60's) and Dutch Princess Margriet who is even older. Both MT and Margriet look good in Natan. Max wears Natan too, but it suits her because she has a womanly figure and she usually wears more daring accessories with her outfits.
Elisabeth looks great in the dress. It suits her age. It's pretty and modern but modest. This maxi dress would look best with summery, sporty shoes like espadrille wedges or strappy flat sandals. The pumps are unsuitable because they are formal dress shoes while the dress is "fun" and casual. I am glad though that she is wearing shoes with modest heels. It suits her age.
I don't think Mathilde dresses like she's 20 years older to better match the age of Phillippe. I think it is just her conservative, very modest style to dress the way she does. Her hair is also equally conservative and modest.