My personal opinion, based on the information in this thread, would be to advocate for a whole-grade acceleration now (skip 1st).

There are many resources available to help him "catch up" in a fun way, at his own pace, over the summer before school starts in the fall.

The research George mentioned may be found at the website of the Acceleration Institute, including
- A Nation Deceived
- A Nation Empowered
- Iowa Acceleration Scale (IAS)