I don't consider CoD kiddies to be "hardcore" gamers in the slightest. A hardcore gamer, to me is someone dedicated to video gaming, who plays what they like, independent of other people's opinions. I consider myself a hard-casual, because the longest I usually spend playing a single game is maybe a week until I get bored and move onto something different, but at the same time, I still have an extensive knowledge of gaming history, and I've been playing video games ever since I could handle a keyboard and mouse (as you may or may not know, I started out with PC games. )
The games that I choose to play usually just happen to be whatever strikes my fancy at the time. I never actually played any FPSs or mature-rated games until I was 12, but I certainly watched my dad play some when I was younger than that, and it just so happens that some of the more violent games he played back then ended up becoming favorites of mine later on (like Diablo I and II, Carmageddon, Duke Nukem 3D). Of course, since I was highly unsure if my parents would have actually approved of me playing those games before I was 12, I mainly stuck with things like various Nintendo franchises (mainly Zelda, StarFox, and Super Smash Bros), fantasy JRPGs, Ratchet and Clank, early Maxis titles, "retro" games (I had a huge obsession with the Atari 2600 and Intellivision for a while ) and other stuff like that. Coincidentally, my mother enjoyed, and still enjoys a lot of those games as well. To this day, I'm still a huge fan of a lot of the games that I played when I was younger, and I honestly think that the ages of 8-11 were some of the best years of my gaming life.