Within many biological populations, individuals differ from one another according to their age. Age-structured models help us determine how such differences affect the dynamics of a population's size and structure. Equations employed in standard continuous-time models include Lotka's Integral Equation, the McKendrick-von Foerster PDE, and the Gurtin-MacCamy Equation. In this seminar, I will discuss some ideas for extending these models to include periodic time dependence, which would be appropriate for populations experiencing environmental conditions that are periodic in time.