There are currently 17.3 million high school students in the U.S. It takes on average 4 years to gain a bachelor's degree in engineering. If Elon wanted to get the top talent he could simply set up the most demanding, elite engineering college in the U.S., handpicking the top 800 talented kids of those 17.3 million. An aptitude test and a promise of employment upon graduation and he'd be good to go for generations. If Elon can't plan a measly 4 years into the future I quite seriously doubt his plans to colonize Mars.