Radiocarbon proxies suggest that the deep waters are poorly ventilated during the Last Glacial Maximum (LGM). Here we use two transient simulations with tracers of radiocarbon and ideal age to show that the deep-ocean ventilation age is not much older at the LGM compared to the present day because of the strong glacial Antarctic Bottom Water transport. In contrast, the ventilation age is older during deglaciation mainly due to weakening of Antarctic Bottom Water transport.