Drinking one or two drinks shows higher estimated BACs (which might relate to more harm due to impairment in reasoning, depth perception, peripheral vision and glare recovery) in a 13 to 18 year old than an adult with relation to body weight. Research shows that at one standard drink, peak BACs ranges from 62.0 mg/dL for 9-year-old boys to 27.4 mg/dL for 17-year-old boys, and from 61.9 mg/dL for 9-year-old girls to 38.2 mg/dL for 17-year-old girls. At two drinks, the estimated peak BAC for girls aged 9-13 exceeded 80 mg/dL (81.8 to 123.9 mg/dL), while only those for boys aged 9-12 reached this level (84.6 to 124.0 mg/dL).
Children and adolescents exhibited higher estimated BACs than adults at each level of alcohol intake since "Both children and early adolescents weigh substantially less than adults and would likely achieve considerably higher BAC levels after five drinks within a 2-hour period or would reach a BAC ≥ 80 mg/dL after significantly fewer drinks" per study by Donovan JE in 2009. A BAC level of 20 mg/dl or higher is considered indicative of alcohol use and BAC levels greater than 80 mg/dL (>17.4 mmol/L) is considered positive for driving under the influence in most states in USA. Per the study, at three drinks, the estimated peak BAC for all children aged 9-17 were 2.3 times greater than the NIAAA binge drinking level for the youngest children (i.e., 186.0 and 185.8 mg/dL for 9-year-old boys and girls, respectively)
At one standard drink, boys and girls could theoretically achieve peak BACs ranging from 62.0 mg/dL for 9-year-old boys to 27.4 mg/dL for 17-year-old boys, and from 61.9 mg/dL for 9-year-old girls to 38.2 mg/dL for 17-year-old girls. At two drinks, the estimated peak BAC for girls aged 9-13 exceeded 80 mg/dL (81.8 to 123.9 mg/dL), while only those for boys aged 9-12 reached this level (84.6 to 124.0 mg/dL). At three drinks, the estimated peak BAC for all children aged 9-17 exceeded the 80 mg/dL NIAAA criterion, and were 2.3 times this level for the youngest children (i.e., 186.0 and 185.8 mg/dL for 9-year-old boys and girls, respectively). At five standard drinks, estimated peak BACs ranged from 137.1 to 309.9 mg/dL for boys and from 191.1 to 309.7 mg/dL for girls, levels that can result in coma and respiratory problems in children and early adolescents.
The more standard drinks consumed at each age, the higher the estimated BAC. Also, the younger the child, the higher the estimated post-peak BAC at each intake level. For ages 9-13, the mean estimated BACs for boys and girls were comparable at each level: mean BACs for girls fell within the 95% CI for boys the same age. For ages 14 through 17, girls had higher estimated BACs than boys at each intake level, with no overlap in their 95% CIs.
RESULTS: The estimated BAC for children after consuming just three standard drinks within a 2-hour period was between 80 and 139 mg/dL for boys aged 9-13 and for girls aged 9-17, indicating substantial potential alcohol impairment. At five drinks within 2 hours, the level used to define binge drinking among college students, children aged 9-13 were estimated to have BACs two to three times the adult legal limit for intoxication of 80 mg/dL.
CONCLUSIONS: Binge drinking assessment in children and adolescents requires substantially lower cut-points than those used for college students. Binge drinking should be defined as 3 or more drinks for 9-13 year olds, as 4 or more drinks for boys and 3 or more drinks for girls aged 14 or 15, and as 5 or more drinks for boys and 3 or more drinks for girls aged 16 or 17.
"The National Institute on Alcohol Abuse and Alcoholism (NIAAA) redefined binge drinking as a drinking pattern that brings a person’s blood alcohol concentration (BAC) to 80 mg/dL or above, a level accompanied by significant physical and mental impairment. For the typical adult, this pattern corresponds to five drinks by a man or four drinks by a woman within a 2-hour period." and definition of standard drink can be found here.
First use of alcohol at ages 11-14 greatly heightens the risk of progression to the development of alcohol disorders per study by DeWit DJ et.al. in 2000. "Body of evidence, however, does suggest that early exposure to alcohol may set adolescents up for problem drinking later on, and that delaying the first drink for as long as possible may help to foster more responsible alcohol habits."
The health risks of youth drinking per NIAAA are
Brain Effects by animal studies — "It’s simply not known how alcohol will affect the long-term memory and learning skills of people who began drinking heavily as adolescents. Scientists currently are examining just how alcohol affects the developing brain, and research has shown that animals fed alcohol during this critical developmental stage continue to show long-lasting impairment from alcohol as they age". Alcohol use during DSM-IV alcohol dependent adolescence is associated with prefrontal volume abnormalities, including white matter differences. Additional research is necessary to know the exact effects of alcohol on the adolescent hippocampus and other brain structures and to better understand the long-term implications of adolescent alcohol exposure.
Liver Effects — "Elevated liver enzymes, indicating some degree of liver damage, have been found in some adolescents who drink alcohol. Young drinkers who are overweight or obese showed elevated liver enzymes even with only moderate levels of drinking".
Growth and Endocrine Effects by animal studies— "In both males and females, puberty is a period associated with marked hormonal changes, including increases in the sex hormones, estrogen and testosterone. These hormones, in turn, increase production of other hormones and growth factors which are vital for normal organ development. Drinking alcohol during this period of rapid growth and development (i.e., prior to or during puberty) may upset the critical hormonal balance necessary for normal development of organs, muscles, and bones. Studies in animals also show that consuming alcohol during puberty adversely affects the maturation of the reproductive system".