1987, some friend gave me a tape with a mashup of Metallica, Helloween and MSG! Haven't stopped since.
I started listening to metal while in high school, since 2010.
I've been listening to metal since I was about 5 or 6. My brothers were into late 90s/early 00s nu metal at the time, so my intro was Korn, Slipknot, and I loved Linkin Park. Eventually branched out a bit further into thrash metal, post-grunge when I was around 9-12, and then into heavier metal (mostly melodic death and prog metal) in my teens.
For me it was since the age of about 12 or 13, my friend in middle-school had gifted me a Cannibal Corpse record, butchered at birth. This was around the time Limewire was still around so I went nuts and listened to everything I could find, what really stuck with me was the album cover and the fact I'd never heard anything like it in my life. I'm about 28 now and I haven't stopped, I became an artist and wouldn't have gotten even close to the success I've had without it. The metal genre is something I'll always hold to my heart.