ऋग्वेदे विश्वासटिप्पन्यः

How late do you think is the पुरुष सूक्त?

This question can be answered thus: the theology/framework presented in it is early-Indo-European having cognates in the Germanic world and Iranic (inferred via lateral transfer to Chinese).

As a sUkta, the 1st 15 R^ik-s form an earlier stratum, with the 16th added later. The 1st 15 themselves might have had an archaic core that was related to the human sacrifice which was already becoming otiose by the time of the earliest vaidika rituals that have come down to us. This core would go back to an early Indo-European age. The 15 R^ik core preceded the compilation of the final ancestral yajuSh and atharvan saMhitA-s.

The later part of it with the word shUdra was clearly after the Indo-Aryans had conquered northern India. Then finally the 16th R^ik with the concept of sAdhya-s as proto-gods was put in place. That corresponds to the “middle brAhmaNa period”.