The correct answer is Developing and using a new kind of prosthesis that simulated real flesh on Crowe's neck, jowls, pate and cheeks
The people in charge of costume design and make up artists found a new material that could look like real flesh when applied properly and this made it possible to make Russel Crowe look much older while still looking like himself. At the time it was revolutionary however it looks very average for today's time as technology was further developed.
