Growing farm size has generally been explained by technological advances that have allowed farmers to substitute capital for labor. Another possible factor in explaining recent farm size is the demographic shift: the age distribution of farmers has shifted to the right and older farmers generally operate larger farms than younger farmers. This paper uses data from the 1982, 1987, 1992, 1997, and 2002 Agricultural Censuses to examine the relative importance of the demographic shift versus technological factors in explaining overall farm size growth. Results indicate that farm sizes tend to increase with age and that, holding age constant, the typical farm-size has increased over time for all ages, presumably due to technological change. The age-distribution shift is combined with the age-specific farm-size shift, to provide a preliminary estimate of the effect of the age distribution shift and technological change on average farm size growth.