I don't remember when I was first introduced to Spider-Man. Some of my earliest memories involve playing with superhero action figures, and Spidey was one of them. Likewise I have no idea when I became aware of Captain America, Iron Man, or Thor. Maybe they were among those old toys, or I saw some old cartoon/s when I was super little. But I've kind of always been aware of them, even if I didn't know squat about them.

I vaguely recall seeing the old Lou-Hulk show on reruns, but not enough to recall any specifics.

Pretty sure my first exposure to the X-Men was the 90's cartoons. Pizza Hut had a thing where if you bought such-and-such, you got a VHS tape with the first....few?....episodes of the show. Fell in love with the mutants right there, and they were among the first Marvel heroes I began following when I got into comics. No idea what my first X comic was, at all, though I think X-Treme X-Men was the first mutant series I seriously followed. Or maybe eXiles?

Actually, I think my first exposure to a lot of Marvel characters was Wizard magazine in the 90's. I got into comics with DC, my entry into Marvel was a lot more stop and go so I probably saw the likes of Clint Barton in Wizard before I saw him in comics.

First Iron Man comic I bought was a random issue (maybe #4?) of the Heroes Reborn run with the Image-y art. First Cap comic I ever bought was, I think, the Winter Soldier trade that came out shortly before the movie. First Thor comic was JMS' first issue. First Avengers was some random issue from Busiek's run, but I had no idea what the hell was going on or who half the roster was, and didn't continue reading (now I'm older, wiser, and trying to hunt down the trades, which is a pain in the ass). No idea what my first FF or Spidey issues were, but the first Spidey I *enjoyed* was volume 1 of Bendis' Ultimate run, and I've yet to meet a FF story I've truly liked, though some have come close and I enjoy the characters on their own or with other heroes.