During the last three decades in the US, the older part of the population has become significantly richer, in contrast with the younger part, which has not. We show that demographics account for a significant part of this intergenerational wealth gap rise. In particular, we develop a general equilibrium model with an OLG structure which is able to mimic the wealth distribution of the household sector in the late 1980s, conditional on its age structure. Inputting the observed rise of life expectancy and the fall in population growth rate into the model generates an increase in wealth inequality across age groups which is between one third and one half of that actually observed. Furthermore, the demographic factors help explain the change of the wealth concentration conditional on the age structure; for example, they account for more than one third of the rise of the share of the elderly within the top 5% wealthiest households. Finally, consistent with a stronger life-cycle motive and an increase of the capital-labor ratio, the model produces an interest rate fall of 1 percentage point.