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Age-related changes in gastrointestinal function have been reported in companion animals, but the impact on digestive efficiency remains uncertain. Healthy dogs (<i>n</i> = 37; 2.6–14.2 years) received four diets varying in total dietary fibre (TDF; 6–29%, as fed). Healthy cats (<i>n</i> = 28; 1–13 years) received four diets with two fat (10–12%; 17–18%) and TDF (9 and 12%) levels. In a crossover design, diets were provided over four consecutive 10-day cycles, including a 4-day faecal collection. Apparent crude protein (CP), ether extract (EE), TDF, calcium (Ca), and phosphorus (P) digestibilities were determined. The effect of age was analysed as a continuous variable in dogs and as differences between adult (1–5 years) and senior (7–13 years) cats. In dogs, EE digestibility was unaffected by age (<i>p</i> > 0.10). Dogs of 6–12 years had higher digestibility of CP (<i>p</i> = 0.032), TDF (<i>p</i> = 0.019), Ca (<i>p</i> = 0.019), and P (<i>p</i> = 0.024) when fed the 6% TDF diet. Senior cats had greater digestibility of TDF (<i>p</i> < 0.01) and Ca (<i>p</i> = 0.024) but had lower EE and CP digestibility with one diet (17% fat; 9%TDF) (age, <i>p</i> > 0.10; diet × age, <i>p</i> < 0.001). Healthy ageing was associated with preserved nutrient digestibility in dogs and cats within the age ranges studied. The effect of ingredient sources in senior cats warrants further investigation.