So when I was younger, my parents made me an authorized purchaser on their Discover card, and gave one to me in case I ever had an emergency (stuck in a snowstorm driving home? Pull over and use our card for a hotel).

Now that I'm older and pay my own way, I was considering removing my name from their account. If I did that, would it make my average length of credit history plummet?

Their discover card is roughly as old as I am, so I'm worried if I remove it my length of credit history will take a nosedive.

(However I was only added to it in ~2006 so it won't be a huge difference if that's when they started counting - I had my first card in about 2008)