Silkies rarely lay that early in my experience. I never expect eggs before they are 9-10 months old, and am not surprised if they are more than a year, although that is not all that common for them to wait that long. Birds that come to about the right maturity during winter often do not lay until the longer days and warmer weather of spriing, adding a few months to the wait.
I just feel very lucky. Every single one of my chickens has started early. I have EE's, Silkies, Cochin's, Plymouth Rocks, Jersey Blacks, Orpingtons, Brahmas, and Australorps. Most started at 16-17 weeks. My Silkies started around 5-6 months. And one of those is broody and sitting on 5 eggs.