Young Americans are showing less interest in buying lotto tickets than their parents, prompting lottery officials to worry about the odds for future growth. While overall ticket sales rose 9 percent last year versus 2015, the number of millennials - adults in their late teens to early 30s - who play is falling.That is creating consternation among leaders of the industry, which generates $80 billion in annual revenue, more than the combined U.S. sales of movie tickets, music and concerts.Only a third of Americans aged 18 to 29 said they played the lottery in the past year, compared with 61 percent for those aged 50 to 64, according to a 2016 Gallup survey.The rate for millennials fell from 39 percent in surveys conducted in 2003 and 2007, Gallup said. For all other age groups, the likelihood of playing went up over the past decade.