> “Our investigation found that Reddit failed to apply any robust age assurance mechanism and therefore did not have a lawful basis for processing the personal information of children under the age of 13… These failures meant Reddit was using children’s data unlawfully, potentially exposing them to inappropriate and harmful content,” an ICO press release said.

Sounds correct to me. They want Reddit to check ages more thoroughly in order to ensure they are dealing with data for under 13s correctly.

Whatever the justification, it seems the UK is determined to push strict age (and thus identity) verification on social sites.