Right away! Dogs are never too young or too old to train!
Effective training methods are taught by dog trainers at many dog obedience schools and puppy preschools at veterinary clinics. Lessons range from basic commands such as sit, stay, drop etc. to more advanced classes involving agility training and fun tricks.
Harsh punishments such as hitting and rubbing noses into their poo and urine is often very ineffective and counter-productive; it makes training in the future even more difficult. Positive reinforcement, using treats and praise, is the cornerstone behind successful puppy training. Please ask your veterinarian or dog schools for more details on training classes.
A successful training program will not only help you train your puppy quickly and effectively, but it will also enormously improve and develop the bond between you and your puppy!