Isn't the verse taking about Muhammad's (PBUH) time? That means these stars were formed and have been working as missiles since 7th century which is 1400 years ago!!!!
Allah says in the Quran :
41:12 "So he ordained them seven heavens in two periods, and revealed in every heaven its affair; and We adorned the lower heaven with brilliant stars and made it to guard; that is the decree of the Mighty, the knowing."
From the above verse we can see that the stars have been guarding the Universe since their inception. Or we might say long before Muhammad (PBUH).
No, it doesn't mean that all stars have been working at missiles since 7th century. It means that a certain position that the Jinns sat in to listen has been foiled by a star. Lets look at the verse again:
''And we used to sit in some of its seats to listen. But whoso listens now finds a shooting star in ambush for him,'' (72:9)^It says in certain positions, they would listen, but that position has been foiled by a star.
Next, the verse you posted does not say that the stars have been guarding the universe since the beginning of the universe and neither does that verse say that new stars would not be formed.