How big do you think my kitten will be when he is full grown?

I have a 3 month old kitten. He is a male and my parents say he seems very large for his age. They keep telling me that he will be a very large cat. He is half Siamese from his mom who was a purebred siamese used for breeding, but his dad is an unknown mix of breeds. Anyway, he is a Polydactyl so he has 6 toes on his front paws, making them quite large. He is 3 months old and currently weighs about 3.2 pounds. He doesn't seen overweight, but very average. How big do you think he will get?