Changes in epigenetic DNA methylation are the most promising predictor of biological age and lifespan in humans, but whether methylation changes affect ageing is unresolved. Here, we discuss converging data, which indicate that one mode by which aberrant DNA methylation can affect ageing is via CCAAT/enhancer binding protein beta (C/EBPβ). This basic leucine-zipper (bZIP) transcription factor is controlled by the lifespan regulator mechanistic/mammalian target of rapamycin complex 1 (mTORC1) and plays an important role in energy homeostasis and adipose tissue differentiation. Emerging evidence indicates that access of C/EBPβ proteins to cognate binding sites is regulated by DNA demethylation via ten-eleven translocation (TET) methylcytosine dioxygenases and their adaptor proteins growth arrest and DNA damage-inducible protein 45 alpha (GADD45α) and inhibitor of growth 1 (ING1). We discuss the emerging causal nexus between C/EBPβ, energy metabolism, and DNA demethylation in organismal ageing.