That might be part of it, but I think based on the abstract they're more trying to say that the amount of stimuli we can perceive in a given moment is limited b

That might be part of it, but I think based on the abstract they're more trying to say that the amount of stimuli we can perceive in a given moment is limited by physical processes that slow down as we age, e.g. your eye movements (saccades) are slower so the mental images you build up from visual input are less as you age, and with fewer mental images/perceptions in any given moment makes it feel like less is happening and therefore time is moving faster subjectively speaking. At least that's how I read it.