I think that is just Tigger's personality and it does not matter at what age you got him. We got our Merlot (our Aby) at Seven months of age and our newest Aby Luna, is seven months and they are absolute loves. We also rescued a 7 week old domestic who is now four years old, had the same love and care as our other cats and hardly lets us come near her.
By law in CT kittens cannot be placed before eight weeks of age, but Helping Paws does not place their domestics until they are 11 or 12 weeks old. And my Aby kittens will never leave their mom before they are at least 12 weeks old. The vet who said they should leave their mom at 7 weeks old does not know the Siamese breed very well - unless the mother is too thin and having a problem caring for her kittens? In that case I would not place them before they were 12 weeks old, but I would let the mom be free during the day, away from the kittens and then have her be with them at night.
I hope you will not place your kittens at such a young age. Please go to www.catsinternational.org
and ask your questions to the experts available on this site.