  Vocal aging, a universal process of human aging, can largely affect one's
language use, possibly including some subtle acoustic features of one's
utterances like Voice Onset Time. To figure out the time effects, Queen
Elizabeth's Christmas speeches are documented and analyzed in the long-term
trend. We build statistical models of time dependence in Voice Onset Time,
controlling a wide range of other fixed factors, to present annual variations
and the simulated trajectory. It is revealed that the variation range of Voice
Onset Time has been narrowing over fifty years with a slight reduction in the
mean value, which, possibly, is an effect of diminishing exertion, resulting
from subdued muscle contraction, transcending other non-linguistic factors in
forming Voice Onset Time patterns over a long time.
