Dear Student.
The major difference in the two ages was that: In the early Vedic age, the King had to share power with Sabhas and Samitis. Majority of decisions were to be taken after consulting the Sabhas and Samitis. Additionally, the Sabhas and Samitis were powerful and the King could not enjoy "Absolute Power".
In the later Vedic Age, however: Nomadic tribes did not have much power. Kingship became hereditary. The King became the most central powerful figure.
Regards