19.
My first Zelda game was
ALttP, but I didn't consider myself a fan until I played
OoT, since I only played it a little
It might be relevant to point out that I got really late to the party, I think
TWW was about to be released by the time I started playing
OoT, wich was the first one I actually finished, still, I was well aware of the existence of Zelda games, mostly thanks to Smash Bros, where I mained Link since before I became a fan.
Then I went around by playing the older games on emulators and whatnot, and a few ones on my GBA,
OoS and
ALttP/
FS to be exact, and when I got my Gamecube late in 2005,
TWW was one of my first games, but I had already beaten around half of the games in the franchise by then.
By the time
TP came out, I had at least played every game.
TL;DR, I'm 19, became a fan with a game older than
TWW, but on
TWW times.