I was 16 and now I'm 20, God I feel old. I really miss the beginning stage of AC:NL everything was really good and fun, plus everything was so new! I like it now as well though, it has really nice updates that enhance gameplay.
My first AC game was Wild World, and I think I was about 6 or 7 when I started that, I'm not sure, but I started New Leaf when it came out - summer of 2012! I remember getting my 3DS for christmas, specifically for New Leaf lol.. I'm 15 now, so i would've been 10
I played my first Animal Crossing game at my neighbor's house when I was about 7...when I was around 11 I got New Leaf but I didn't really understand how to play completely for a couple years