Some reading for me:

http://www.cam.ac.uk/research/discussion/school-starting-age-the-evidence

https://www.psychologytoday.com/blog/freedom-learn/201505/early-academic-training-produces-long-term-harm

Interesting that the one below comes from the NEA:
http://neatoday.org/2015/06/19/the-reading-rush-what-educators-say-about-kindergarten-reading-expectations/