I have no idea how old I was, it was around the time that my cousin got an amiga, if that helps you.
It was of course, Monkey Island. I played for a while and then I had to go home. But around a year later, around the same time I got my first PC, whilst shopping in HMV, I saw Monkey Island for sale. I instantly bought it. Then bought many others.
And we all lived happily ever after.