Wattles start to come in around 6-8 weeks. When they are young wattles in pullets don't grow very fast and are small while in cockerels they grow faster. At 8 weeks, I would still say pullet until further notice as they are still pretty small.
Behaviour isn't always a good indicator of pullet vs cockerel at least when they are young. Their personalities are still developing and they are also constantly figuring out the pecking order. I personally would never put any weight on behaviour to determine pullet vs cockerel until they are older.