Crappy auto flowers!
Autos start flowering at between 3 and 5 weeks of age, regardless of size, and this is not due to bugs or anything else, just purely the age of the plant.
If you are interested in getting decent yields from genetically stable and well sorted plants, stick with photoperiod fems and you will never get 3 inch seedlings flowering, especially if you grow outdoors.
Autos really need to be grown indoors with mega lights, an 18/6 light/dark schedule and probably hydro or coco coir (pseudo hydro) to get any sort of acceptable results, - they really don't perform all that well outdoors. Fine if you are happy with 1-3 foot tall plants and a few grams of bud, but in the same time frame you can grow a 5-10 foot photoperiod fem that will give you half a pound or more!
Hope this helps, Organoman. (and enemy of auto flowers!)