In many population, the behavior of individuals might differ according to their age. This structure of the population have profound influence on its dynamics as well as its genetic diversity. I will first investigate the inside dynamics of expanding solutions to integro--difference equations with stage--structure. I will show that the presence of the structure in the population might modify the nature of the expanding solutions at its leading edge. In particular, expanding solutions with age--structure are pushed in a local sense while in absence of age--structure those solutions are pulled. This work is in collaboration with N Marculis, R Lui and M A Lewis. In a second part, I will investigate the dynamics of the genetic diversity in metapopulations. I show that the age--structure might have profound influence on the local diversity of sub--population composing the metapopulation. This work is in collaboration with P Lafontaine.