<Li> One size fits all--Another commonly used system suggests that the first two years equal 10.5 years each, with subsequent years equaling four human years . This is more accurate but still fails to allow for size / breed, which is a significant factor . </Li> <Li> Size / breed specific calculators--These try to factor in the size or breed as well . These are the most accurate types . They typically work either by expected adult weight or by categorizing the dog as "small", "medium", or "large". </Li> <P> No one formula for dog - to - human age conversion is scientifically agreed on, although within fairly close limits they show great similarities . </P> <P> As a rough approximation, the human equivalent of a one - year - old dog is between about 10 and 15 years--a one - year - old dog or cat has generally reached its full growth and is sexually mature, although it might still be lanky and need to fill in a more mature musculature, similar to human teenagers . The second year is equivalent to about another 3 to 8 years in terms of physical and mental maturity, and each year thereafter is equivalent to only about 4 or 5 human years . </P>

How old is a 7 year old dog