
there was a recent thread that covered this issue. [Link]http://www.champdogsforum.co.uk/cgi-bin/board/topic_show.pl?pid=251405;hlm=and;hl=12%20weeks#251405[/Link]
It was quite a hot topic. I think the opinions expressed showed that it soews depend on the breed. Most people would consider 6 weeks too young.
Puppies that are well grown and advanced seem to start going at between 7-8 weeks old, and some small delicate breeds are best homed later.