The repeatability of longitudinal measures of whole blood DNA methylation (obtained using the Illumina 450k chip) was assessed in two cohorts of ageing. The Lothian Birth Cohort of 1921 and the Lothian Birth Cohort of 1936. Data were collected at ages 70, 73, and 76 (LBC1936) and 79, 87, 90 (LBC1921...