This paper addresses the open question formulated as: Which levels of abstraction are appropriate in the synthetic modelling of life and cognition? within the framework of info-computational constructivism, treating natural phenomena as computational processes on informational structures. At present we lack the common understanding of the processes of life and cognition in living organisms with the details of co-construction of informational structures and computational processes in embodied, embedded cognizing agents, both living and artifactual ones. Starting with the definition of an agent as an entity capable of acting on its own behalf, as an actor in Hewitt Actor model of computation, even so simple systems as molecules can be modelled as actors exchanging messages (information). We adopt Kauffmans view of a living agent as something that can reproduce and undergoes at least one thermodynamic work cycle. This definition of living agents leads to the Maturana and Varelas identification of life with cognition. Within the info-computational constructive approach to living beings as cognizing agents, from the simplest to the most complex living systems, mechanisms of cognition can be studied in order to construct synthetic model classes of artifactual cognizing agents on different levels of organization.