By looking into the structure it will be really difficult for anyone to say which Maven Archetype was used to create the code repository. However if you want to make sure that you are using the latest Maven version for all the dependency, you can create a new AEM project using the Archetype 26 and reference to the POM files generated with your old code base to see exactly which version you need to update.
As you know the latest Maven Archetype(not only 26 others as well) has a different structure all togather i.e. it has now so may folder specific content such as ui.config, ui.frontend and so on. you will need to create a new project and migrate the code from old project to Latest Maven Archetype.