I don't know about an old B&W movie, but apparently a movie based on his life was made in the 1980's: Too Young the Hero
At 12, he was still a child. The lowest age I'd heard about was 14, which also was far too young.
Might be that. I might have seen it in color but so long ago that in the haze of my memory I recollected it as a B&W film.