In the process of updating the first forest inventory of implanted species in Argentina, stratifying by age class was recommended. The possibility to estimate age classes using Landsat 5 satellite data, was studied due to lack of information regarding this variable for every stand. This study was done over an area of Corrientes Province. The relation between age and digital number values, reflectance values, Tasseled Cap transformation and different vegetation indexes, was analyzed for eucalyptus (Eucalyptus spp.) and pine (Pinus spp.) stands. A significant correlation was found between reflectance values of band 4 and the age of eucalyptus (r = –0.58) and pine (r = –0.79) plantations. Equations were constructed in order to predict ages of stands of both genera. These equations estimated age with a mean error of 2.2 years for eucalyptus stands and 3.5 years for pine stands. Baring in mind these results and the stratification by age needed for the mentioned inventory, it is advisable to set two age classes for the age range studied, for both genera.