If young Weyland looked like Peter O'Toole it would explain why he (being such a narcissist) was so obsessed with the character Pete played in his most famous film so having the same actor play Weyland as an old man makes perfect sense.
I have been calling Weyland, Guy-Guy Pearce since seeing the film, as his first appearance in the film wrecked the mood of the lovely first 10 minutes or so (not that Jar-Jar was the first thing wrong with TPM).