White silkie chick with comb male or hen or rooster

[lauriefishies]

Even though I bought this chick as a purebred silkie. I'm pretty sure it cannot be or it has bad genes. It enormous! Its almost the size of my Naked neck hen and is bigger than my Silver Laced Wyandotte of the same age. He or she does have the 5 toes on the feet but has a single black comb. Still not sure of sex but it likes to chest bump the others with cackles flared out but squats a bit when I go to pick it up. Can silkies be vent sexed accurately at three months old?