I'm no expert, but it sure looks like the nitrogen deficiency shown on this site.
http://www.bihydro.com/calc-deficiencies.php
It's a pretty good little module that shows pictures for common nutrient deficiencies.
I have three lowryder diesel ryder (feminized autoflowering) plants going that are just starting into week 5. Two out of the three began flowering in week 3, but the third has still not autoflowered. All 3 have been in exactly the same enviroment for the entire grow. (My journal has some info...