I do not think he will walk free.
His age has been confirmed after going through his school records. Hence, termed juvenile.
Now how the govt wants to proceed and what laws needs to modified to ensure he is punished is still pending.
I doubt that can happen while the case is running. It would be "twisting the law"; if they do an amendment. As per the technicality; he cannot stay in the juvenile home once he hits 18, and cannot be tried further. I guess it is: a loop-in-the-law + double jeopardy.