I started about 3(or was it 4?) years ago. I already had roughly 40 games in total including all my systems (since I never sold anything other than some N64 and gamecube games), but I wasn't really "collecting". It really started when I was looking at my few NES games, and thought "Wait, I don't have Crystalis, wtf?", and now... well... just look at my collection
Thank you Crystalis
Even then, I didn't really realize I was collecting until I woke up one day with 100 NES games in my room
It helps that, at that time, I found jjgames.com, which had much cheaper prices at the time, and free international shipping on orders over 25$ (they don't anymore, so I pretty much stopped ordering from them).