At least 10% of the global population is impacted by chronic kidney disease (CKD) and ageing is a key risk factor. CKD is characterised by the build-up of extracellular matrix and a loss of functional nephrons. However, the mechanisms that maintain matrix homeostasis across the physiological lifespan remain elusive. Using 13C-lysine metabolic labelling, we quantified kidney matrix protein turnover in healthy mice at four timepoints (8, 22, 52, and 78 weeks). We found that basement membrane components, including collagen IV, laminin-521, nidogens and perlecan, were more long-lived over age, with collagen IV half-lives extending from weeks in young kidneys to years in aged kidneys, suggesting a reduced capacity for basement membrane renewal. The half-lives of fibrillar collagens I and III also increased over age up to forty-fold, which is consistent with minimal degradation. In contrast, collagen XV retained rapid turnover despite increased abundance, indicating a persistent role in tissue remodelling. Using peptide location fingerprinting to predict structural alterations and proteolytic processing we identified age-dependent meprin oligomerisation and altered nidogen–laminin interaction states. We predicted structural alterations within assembly domains of collagen VI and reduced accessibility of integrin-binding regions, suggesting altered microfibril organisation and cell-surface binding. Collagen XV had predicted structural changes across the NC1 domain encoding the matrikine restin, indicative of altered protease accessibility and matrikine release during ageing. These findings are consistent with age-related kidney fibrosis being driven by impaired matrix degradation rather than increased synthesis, with protease accessibility and altered matrix interactions likely contributing to this remodelling process.