The age of the baby in the question would probably be 12 months old. This is because Baby Lee is experiencing active experimentation, which in the Piaget Cognitive Development Theory, refers to the Sensorimotor stage.
Baby Lee would experience this stage until he is 2 years old. The Sensorimotor stage itself is divided into six sub stages (reflexes, primary circular reactions, secondary circular reactions, coordination of reactions, tertiary circular reactions, and early representational thoughts) and Baby Lee is currently in his fifth stage – tertiary circular reactions. This is because he is now experimenting from one object to another to learn more about the objects surrounding him.