Data on age at first tobacco smoking were available for fewer countries; nonetheless, among those aged 22–29 y, an estimated 46% of young adults in the Ukraine had started to smoke by age 15 y, and 72% by age 21 y; similar estimates were obtained in the US (44% and 72%, respectively). Nigeria had the smallest estimated cumulative incidence proportion for tobacco smoking by age 15 y (7%), and the following intermediate estimates were observed: Israel (9%), South Africa (11%), Colombia (12%), Peoples' Republic of China (15%), Lebanon (18%), Mexico (21%). The rank ordering of countries with respect to use by age 21 y was almost identical (Table 3).
