Many people are aware that dog years and human years are not equivalent. There is a ratio of human years to dog years that is used to calculate how old your dog is in human years. Each dog year is equivalent to 4 to 7 human years.
Large dogs will always age faster than smaller dogs, so if you have a large dog, each of your human years is more like seven dog years. Small dogs can live into their late teens quite frequently, while big dogs are often quite old at ten.
The kind of care and exercise and food that you give your dog can significantly impact their lifespan, but there are still some limitations to the age that your dog will reach, especially if they belong to one of the larger breeds.