Here's my timeline:
64 - Never played this one when it came out. I didn't have a N64 and Smash 64 came out a few months before I was born. I later got it on the virtual console when I was about 10, but I never played much of it, as I figured there was no reason to when I could just play Brawl.
Melee - My first exposure to Melee was when I was about 5 or 6, my cousin offered to play it with me, but I said I couldn't because it was rated T and I wasn't a teenager (I know, lame move on my part). I later picked up a copy when I was 7 or 8, right when I was getting into Pokemon, as I thought a game with both Mario and Pokemon in it was the most amazing thing I ever heard of. At the time, the only characters I knew were the Mario and Pokemon cast.
Brawl - I first discovered Brawl was a thing when I was on Squirtle's wikipedia page in early 2008. I got the page about Squirtle and Pokemon Trainer's upcoming inclusion in Brawl, and little Garteam was never the same when he found there was a Smash game coming to Wii. Every month I would go with my Dad to the local Rogers (Canadian technology store that used to rent games and movies) and ask if they had a copy of Brawl to rent, only to find out the game wasn't out yet. Eventually, my persistence payed off, as I finally rented Brawl when I was 8 and bought it shortly after. By this point, I had played Kirby and Legend of Zelda, so I knew those characters from then on. However, most of the roster was largely unknown.
Smash 4 - I remember when Smash 4 was announced in E3 2013, I was 13 and just coming home from school that day when I saw the news. By this point, I had either played most series or had learned about them through Smash speculation, so I had at least a decent knowledge of who each character is. When I was 15, my Dad came home with a copy of Smash for Wii U, a Gamecube controller adaptor, and a new Smash Bros Gamecube controller.