The 8 is something Wolfman made up in NTT, in the Batman comics he was usually older.
I think in the version of his Origin Story published around that time he was irrc 10 when his parents died, Year 3 (the Story Arc before A Lonely Place of Dying) indicated iirc that he was 11, and in most later Batman comics put that age at 12.
The 8 never made much sense, Dick is never shown to be that young in comics set at the beginning of his career, and it would have made Batman already close to 40 at the time of A Lonely Place of Dying.