Selecting breeding animals at younger ages reduces generation interval, but also increases risk for long term profit because selection is less accurate and for management decisions because there is more variation in early reproductive performance of ewes. This study simulated different flock age structures and young ewe fertility levels in Merino breeding programs and compared average genetic gain and variation in genetic gain. Genetic gain increased by 18% when ewe fertility at 1 year of age increased from 10% to 90%. Age structure mainly influenced the risk of a particular breeding program design, as measured by increased variation in outcomes. Early selection in one or both sexes increased risk due to low accuracy of selection. The recent advent of breeding values utilizing genomic information presents opportunities to increase selection accuracy at younger ages and reduce the risk associated with early selection.