かっていうので is used to provide additional information or clarification about something that was just said. It's a way of saying, "if you don't know what I'm talking about, it's because it happened a long time ago." Here's an example: 今日は寒いかっていうので、ジャケットを着てきた。 "It's cold today, so I came dressed in my jacket." ジャケットは昔使っていたものです。 "The jacket is one that I used to use a long time ago."