In Chinese tradition, the number 18, normally 十八 (shí bā), can also be read as 幺八 (yāo bā), which sounds like 要发 (yào fā), meaning
that one is going to prosper. Thus, building floors numbered "18" are often very expensive in China

The Hebrew word for "life" is חי (chai), which has a numerical value of 18. Consequently, the custom has arisen in Jewish circles to give
donations and monetary gifts in multiples of 18 as an expression of blessing for long life.

Both from the always wise wikipedia. I didn't know that there was any significance to the number except that you can drink in the UK and that your
tried as an adult in the court of law in the states.