This would be the Dragon Age RPG. I bought the first two boxed sets when they came out, but never played them, despite being very intrigued by the mechanics (especially the stunt mechanic which I’ve often thought about porting into my D&D 5E game, but that would require me to make rules, and if you’ve been reading this month, you know how I feel about that).
This was a surprisingly difficult question, because I don’t have a record of when I purchased many of my RPGs and this question is not to be confused with the oldest RPG I have but not played (because I recently acquired a 1974-vintage original D&D set), of course. Now there are MANY RPGs I have that I’ve had a long time and haven’t played in even longer, like Marvel Super Heroes. I have played them, though, it’s just been 20+ years.