I am probably showing my ignorance here, but right now I cannot think of any popular young metal bands.
Let me define popularity. I will consider a band to be popular if since the beginning of 2015 it has released at least one album which has been certified silver or above in at least one country, or which has reached the top three in the album charts in at least one country.
So far I have found: Avenged Sevenfold, Black Sabbath, Deep Purple, Eluveitie, Iron Maiden, Judas Priest, Metallica, Nightwish, Ozzy Osbourne, Sabaton, and Scorpions. This list does not include either AC/DC or Megadeth, although most of us would want to include them in our list of popular bands on other grounds. AC/DC tee shirts still sell like hot cakes. The Dave Mustaine V was the most popular guitar in the world just a few years back.
All of those bands are at least ten years old. In fact, most of them are positively ancient.
Can anyone name me a metal band which is less than ten years old, and which can claim to be popular?