Check out his spurs. On a youngster they will be not much more than buds. By the time he is two he will have longer spurs (unless removed). On a year-old bird they might be as much as a 1/2" long. Also, younger birds tend to be leaner--they fill out as they mature. I would say that a lot (not all) silkie males don't reach full maturity until they are close to 3 years.