Congrats on your new pullets. Do you currently have any other hens?
CLBs are an autosexing purebreed, so point of lay (POL) will be up to 36 weeks, though generally speaking between 26 and 30 weeks is average. 20 - 22 weeks is very early, even for a hybrid layer, so I wouldn't hold your breath... but with hens you never know!
A lot of hens do take a break during the winter as there isn't the amount of daylight to stimulate the laying. However, during their first winter (so for your pullets, it will be next winter) they will often lay more regularly, or stop for a shorter period of time.
I believe CLBs lay between 150 and 180 eggs per year, and although the predominance is for pale blue eggs, they may also lay an olive coloured egg.
you can keep feeding growers right up until they lay their first egg. Limit corn/maize to about one smallhandful between the three per day, and you're doing fine with the once weekly spaghetti treat.
As they are still young, it is an ideal time to get your pullets used to being handles. Pick them up and check them over regularly for unwanted visitors. Personally I don't treat for nasties until I have to, as I believe that over use of chemical deterrants will lead to resistance. Having said that, no harm in chucking some mite powder in a dust bath occasionally
I would worm from about 6 months on. if you decide to go down the "natural" route, please still do use a chemical wormer (flubenvet) once a year.