Why does coffee keep you less awake as you get older?

Il Corriere della Sera (Daily / Italy) 

Come mai con gli anni il caffè tiene meno svegli (Why does coffee keep you less awake as you get older?)

A study just published in Nature Communications Biology by researchers at the University of Montreal has analyzed the impact of caffeine on sleep on older people. The reduced arousal effect can be explained by a reduction in the number of certain receptors on which it acts and by the fact that the brain's sleep architecture becomes more disorganized in older age (and therefore the impact of caffeine is lessened).