For most chickens it would be normal for them to begin layin at 19 to 20 weeks. It would not be unusual, depending on the breed for them to start at 18 weekls. 16 weeks is early for any chicken especially silkies and for all of them to start this early at the same time leads me to believe that they are older then you think. As far as being egg bound, it is common for that to happen when they first start laying and it is a good idea to watch them so you can spot a problem and attempt to resolve it before it is too late.