  It is a commonplace perception that speed of time subjectively experienced by
humans significantly differs from chronological (objective) time and shows a
great deal of variability. An often cited example is the phenomenon of the time
acceleration with age - subjectively, the time passes faster as we get older.
While the exact mechanisms behind it are not yet fully established, here we
consider three 'soft' (conceptual) mathematical models that might be applicable
to the speeding time phenomenon: two proportionality theories widely discussed
in the past and the original model that takes into account the novelty of
experience effect. The latter is found the most plausible, as not only it
satisfactorily describes the decadal subjective time acceleration, but also
offers a reasonable explanation of the human life experience accumulation with
age.
