Because you are not 'legally' an adult until you reach that age and that is the age that the lottery commission sets the age limit.
18.
18 years or older.
the legal age is 18 years of age
18 years of age
18
The legal gambling age in New Jersey is 18
18. (when you're 18, you're pretty much an adult)
18
In the US you must be at least 18 to play the lottery.
18 years of age
You must be 18 years of age. http://www.ctlottery.org/rights.htm
It depends on local legislation. Few of which agree. The seller has to be 18 in some places, whereby the buyer may be 16. Some countries have no restrictions.