I think this is an interesting approach to tackling the "puppy mill" problem.
A Maryland Senate Bill would ban the retail sale of dogs less than nine months old. It would not apply to breeders that do not sell through retail pet stores or shelters.
No large-scale breeder selling to pet stores will spend the money necessary to raise puppies until they are 9-mos-old. That's not cost-effective. The profit is in not having to feed and really spend money on puppies who can be sold at 5-9 weeks of age - mom does the hard work, and the breeder need only feed her.
So, this in effect, would put any puppy mills wishing to sell in retail stores out of business. If there are pet stores whose primary profits are from the sale of puppies, they will either go out of business or re-evaluate their "products".
Certainly large-scale breeders could sell animals through the internet or other non retail store venues, but I think this is a pretty creative approach to a very real ethical problem.