The old adage "you can't teach an old dog new tricks" is not true -- you can teach an old dog new tricks, and you can teach a young dog new tricks too. Puppies eagerly learn, but not all puppies learn at the same rate; some are a little quicker than others.
Puppies are generally taken from their mothers and placed for adoption when they are 8 weeks of age. This may seem young, but having had a full two months worth of mother's milk, which strengthens their immune systems, and mother's discipline, which helps socialize them, they are ready to go out into the world. Puppies at this age should not be expected to hold their bladders or bowels for more than 30 to 45 minutes when they are very young. As they age, they develop more control. A reasonable expectation for a reliably potty trained puppy is 6 months of age. Some catch on more quickly, some take a little longer.
At about the age of 12 weeks it's important to get your puppy into a puppy kindergarten class. This will facilitate his learning, reinforcing skills he is learning at home and teaching him critical new skills. Socialization is important because other puppies can help you teach your puppy. For example, if your puppy plays too rough, the other puppies will learn to avoid him, and eventually he'll figure out that his biting and horseplay are too rough. This lesson is learned in class, but practiced at home. If you are taking your puppy to kindergarten classes, you can expect him to learn about basic manners and some basic skills, such as sit, by the time he is 14 to 16 weeks old. If you are training him on your own, it may take a little longer.
Birgit Edler, owner of Canine College, a South Florida dog training facility, explains that puppies learn much more quickly than adult dogs. "It's like when computers first came out," she says. "Older people who grew up without them were able to learn to use them, but younger people growing up with them learned much faster." She points out that you can begin training at 8 weeks of age, and your puppy should be well-versed in basic skills like sit, stay, come and heel when she is about 4 to 6 months of age. Canine Companions for Independence, an organization that raises and trains service dogs, begins training puppies at 8 weeks of age. This early training prepares the puppy for an extremely high standard of training, one that most companion animals, if not trained the same way, would never reach.
Each dog is an individual and, like a child, learns at a different rate. Many influences come into play when determining how much you can expect from a particular puppy at any given age. Some breeds of dog, such as the poodle and Australian shepherd, are notoriously bright and catch on to training very quickly. A typical poodle puppy can be reliably house-trained in just a few days. Dogs who are less clever, or those who have a stubborn streak (you know who you are, terriers), may take a little longer. Expectations also depend upon how diligent you are in your training. The more lax you are, the more time it will take, regardless of the dog's intelligence.