Wow! So how did that happen? Because, you know, millennials are now adults? Of course it's going to be a millennial taking your job if you are not a millennial: Millennials are younger than you.
There's nothing particularly abnormal about the current moment in the labor force. Over the past seven decades, the age ranges of the labor force have largely followed the baby boom. As the boomers got older, the age ranges they covered swelled.
If you look at age ranges as a percentage of the labor force, you can see that ripple as well.
But notice the ranges 18-19, 20-24, and 25-34 on that chart. Those three combined comprise more than a third of the total workforce. And millennials, under most definitions, are those born from 1980 to 2004 -- meaning all of those age groups. That's 23 years, compared to Gen X, which is usually considered to be about 15 years of births. So, yeah, there are more millennials.
(We've noted before that Pew's generational definitions aren't the same as others. Also that "generations" are made up.) (Update: A good point here, too -- just because they're in the labor force doesn't mean they're employed.)
So the point is this: More people born from 1980 on are in the workforce now, because those people are now old enough to hold jobs, making memes and apping iPhones and so on. In a few decades, we'll see stories about how the next generation, the kids being born now and who have no generational name yet, are taking all of the jobs. Because generations die out and are replaced. C'est la vie, quite literally.
Unless, of course, Generation No-Name is replaced by robots. Which is possible. That's what all the millennials are trying to invent.