I officially began playing video games when I was, like, 6 or 7, when my parents got me a GameBoy Advance for Christmas. I've been exposed to the Legend of Zelda before then, because I would always watch my mom play the original one--as well as a few other games--on the NES from time-to-time when I was younger. But, since the question was what age was I when I actually began playing, it was around probably the second year of having my GBA, and it was probably near the end of my second grade year.
A Link to the Past was my gateway drug game to the series, even though I had the opportunity to start with the Legend of Zelda--which I did start playing awhile after starting my file in the former. I don't think the true attachment to the series really sparked until third grade--which was along with my love for Hamtaro, so they kind of were, like, ever-clashing until fifth-sixth grade. That would make me about 10 when Hamtaro stopped neutralizing my love for the Legend of Zelda. xD I just never took actually beating the games seriously until I was, like, that age. xDD
But yeah... I was around 7 years of age when I started playing. I kind of like the fact that... even though I'm kind of young, I got to grow up with an NES so I still consider myself an old-school gamer. <3