All chickens will lay at different times. There is really no telling.
I have some that are 30 weeks old that have still not started laying yet.
I had some start laying at 24 weeks and none before that age.
Some others here have had theirs lay at 18 or so weeks.
You really cannot say that silkies lay at such and such age. It does not go by breed.
I havve silkies that are 6 months old and not laying yet.
I have sex links who alot of people say lay early, mine laid at 24 weeks.
So anyway, you just have to be patient and wait it out.
This is also not the best time of year for chickens to start laying, with the colder weather and shorter days.
You did not say how old your chickens are.
"Most" will not lay before 18-20 weeks.
It doesn't really matter how "big " they get for them to start laying.
You should probably notice some signs when they are getting near laying age, their combs and wattles will get really bright red, they will crouch down or squat when you come over to them or pet their backs and some will start sitting in their nest boxes for a couple of weeks before.