Also, apparently this guy (Alan Webb, an authentically elderly actor born in 1906) was the original choice to play the Emperor back in 1982. Ian McDiarmid was the runner-up. But Webb fell ill (and actually died later that year) so McDiarmid got the nod.
Oddly enough, a couple decades earlier Webb had turned down the part of a crazily-dressed alien doctor on some BBC children's program. The role went to a guy called William Hartnell instead.