O envelhecimento afecta a capacidade de absorvermos estimulantes nas bebidas (o que significa que quanto mais velhos formos mais cuidados devemos ter com cafeínas e afins e as horas limite para as tomar - se não quisermos efeitos adversos no sono):
Stimulants in the drinks takes longer to absorb in the over-50s | Daily Mail Online
Citando:
"Over-50s take longer to absorb stimulants in tea and coffee, scientists say;
Two coffees after lunch could leave equivalent of one cup in the system by 8pm;
Traces of caffeine in the body at nightfall can wreck the chances of drifting off"