Where are you getting your scores from? (If it is a free score from a credit card, tell us the name of the card. It might be a web site like Credit Karma, Credit Check Total, etc.)
I notice also that you mention only one score. You should be looking at three different scores, each drawn on the data from a different bureau. (Experian, TransUnion, Equifax.) Each of these scores will have a report associated with it. There are ways to get frequent reports for free from all of the three bureaus.
You mention that you have not closed any accounts or opened new ones. Assuming for second that the score is a true FICO score (and it might not be) closing an account should not affect the age of your profile, nor would opening a new one. Closed accounts in FICO count just as much for the scoring factor "Age of Oldest Account."
What might have happened is that an old closed account has dropped off your reports and now your Age of Oldest appears much less. To figure out if that was the case, you'd need copies of your report from a few months ago and then you'd pull a fresh copy based on the bureau's data today.
Also possible is that you are dealing with a non-FICO score. The good news there is that lenders and CC issuers don't care about non-FICO scores.
