Can A 6-7 Month Old Male Dog Impregnate An 8 Year Old Female?

Yes he could!  And I know an experienced dog breeder who was caught out by this!  You don't really want an 8 year old bitch having pups - she is equivalent to a woman in her fifties!  If they mated today then get her along to the vets for a "morning after" contraceptive injection, then keep them apart until you are sure her season is over.

It is possible that your male dog is fertile.  Onset of puberty is influenced by breed, nutrition, environmental factors like how many dogs in the household, disease and stress.  Small breeds generally mature at 6-7 months and giant breeds at about 20 months.  

Also, the female needs to be on heat for pregnancy to result.  If you suspect your female is pregnant you should take her to the vet for testing.  They can tell you after about 18 days after onset of heat.  You should separate the dogs until then.