Something bothers me about the example - perhaps my lack of exposure.
[As] young as he is, he has already mastered three foreign languages.
I'm used to hearing this introductory phrase leading to a cautionary, not some statement of praise.
Young as he is, he should not be drinking so much.
Young as he is, he hasn't the experience to tackle a job like this.
(Since/because he is so young, he should not be drinkng so much.)
Young though he may be, he has already made his first billion. (This is okay by my ear.)
I'm wondering if the "optional as" makes a difference in this respect.