The puppy should be at least 2 weeks old and ideally should be treated at the following weeks of age: 2, 3, 4, 6, 8, and 10. Don't forget to treat any adult dogs in your home monthly or at least twice a year.
Puppies can be born already infected with worm larvae from the bitch. Worming should start at 2 weeks old and continue every 2 weeks until they are 12 weeks old
Puppies are usually given their first dose of wormer medicine within the first few weeks of their life since most puppies have parasites when they are born.
Pups should be six weeks of age before they are wormed the first time. Most OTC products only handle hook & tape worms. I recommend something from your vet.
It's different, depent on dog species... But we can give wormer medicine at around 2-3 month... You must give medicine that for child (usually in fluid form). You can use pipe of injection, it makes easier to give.