Hi Sable,
The DNA profile that AKC has on-record is only for identification purposes. It doesn't indicate any genetic predisposition to disease - it's just a "fingerprint" that allows AKC (and others) to verify paternity if there is any suspicion. DNA profiles must be on-record for frequently-used sires, imported sires, and sires whose semen is shipped (you can see where verifiable paternity is necessary in these cases). DNA is only required for a dam who is involved in a litter that is registered as having multiple sires (that could be the subject for a whole 'nother thread!).
As to the minimum age for breeding... The AKC is very laissez-faire when it comes to this sort of thing. The eight-months-old requirement is, I believe, fairly recent (past 15 years). Please remember that the AKC is NOT in the business of assuring the quality of breeders or dogs - it IS in the business of getting dogs registered, and a large part of its income comes from so-called "high volume" breeders (ie. commercial puppy mills selling to pet stores). "AKC-registered" is generally a good thing in a puppy, but it is in no way a guarantee of quality or health.
If you discover that the mother of the puppies you're looking at is younger than you think she should be for breeding, don't buy one of those puppies (and tell the breeder why you didn't).