Closing a card doesn't affect your average age of accounts, which is what everyone is talking about when they say "closing" a card hurts your credit.

FICO08 factors closed cards into your average account age, until they fall off 10 years from closing at which point they are obviously no longer included in the average.

Never close your oldest credit line if you can avoid it, because in 10 years that WILL hurt your credit history.

FICO 8 calculates "average age of accounts" as total months of all accounts on your credit report (open or closed) from the open date of the account to the present and divides that by the number of accounts.

A closed credit line will drop off your report after 10 years after you closed it (or is it 10 years after open date? I don't know which!)