That clarification needs a little further work. A player in the U.S. needs to be 1 year removed from his high school graduation, and if he's 17 when he graduates, he can play in the NBA at 18. International players must be 19 by the calendar year in which they are drafted, so if they were born in November or December, they can also play in the NBA before they turn 19.
The rule seems unreasonable. It appears that 19 year-olds graduating from high school can't play right away, but some that are younger than that can play in the NBA. Stern seems to have designed the rule to get the NBA scouts out of the high school gyms, which is a valid goal. But the rule seems somewhat unfair, and I wouldn't be surprised to see it legally challenged by some player who will be 19 when he graduates.
cbs.sportsline
SAN ANTONIO -- When commissioner David Stern announced the NBA's minimum age had been raised from 18 to 19, he was being overly simplistic and inaccurate.
Under terms of the new six-year collective bargaining agreement, there could still be 18-year-olds playing in the NBA.
Previous eligibility rules stated that American players could not become draft-eligible until their high school class graduated -- wording that allowed some players to enter the league at 17. The new rules mandate players to wait one year after their high-school class graduates, meaning that players born in November or December could be appear in NBA games prior to their 19th birthday -- provided they graduated at 17.
Rules for international players also changed. Previously, a foreign-born player needed to turn 18 before the draft. Under the new rules (which will not affect this year's draft next Tuesday in New York), international players must turn 19 by the end of the calendar year in which they become draft eligible -- again leaving a two-month window in which an 18-year-old might be playing in the NBA.