['Although alcohol drinking onset in younger people is associated with an increased risk of alcohol-related injuries, other factors, such as habituation and susceptibility to alcohol, in the process of aging have not been adequately examined in animal models. In the present study, we determined whether age of drinking onset affected alcohol drinking behavior and led to alcohol tolerance in experimental animals, and extrapolated some of the findings to human alcohol drinking patterns.', 'In the first experiment, 18 rats that were naive to alcohol were tested at the age of 1, 4, and 10 months with 4 hr of access to 10% (v/v) alcohol. After the time access tests, these animals (1, 4, and 10 months of age) were housed individually and given free access to 10% alcohol solution and tap water. At 3 and 6 months later, all rats that had experienced alcohol drinking were studied for the voluntary consumption of the alcohol solution, alcohol preference, under the two-bottle method in a second experiment.', 'In the 4-hr alcohol-access test, alcohol intake (g/kg/hr) was significantly increased at 0.5 and 1 hr in 1- and 4-month-old naive rats compared with 10-month-old naive rats. The daily alcohol intake (g/kg/day) of rats with drinking onset at 1 month of age was significantly increased at 3 and 6 months after the voluntary alcohol consumption. The daily alcohol intake in the rats with drinking onset at 4 months of age was significantly increased at 6 months only. However, the daily alcohol intake did not change in the rats with drinking onset at 10 months of age through the alcohol preference test.'] Does increase of rat alcohol drinking behavior depend on the age of drinking onset?