I'm 41. Implausibly, the first thing I read was Giant Size X-Men at the age of about 7 or so round another kid's house. I only realised the significance of the book many many years later, and at the time was mostly confused at whether I was supposed to know or care who the old characters who were getting shitcanned were.
A few years later I read part of Mutant Massacre (with Piotr throttling the whirlwind guy, who was kind of a dick), which was a back-up story in the Transformers UK comic, then a while after that a mate had all of X-Tinction Agenda, and then the animated series came out.
Eventually I got around to reading the comics, which I think I was probably supposed to have done in the first place.