Are you sure they approved you with vw? They may have shopped you around. Whats your credit reports say?
As a previous Finance Manager I'm going to take an educated guess at what may have happened...
The F&I guy probably loaded the deal...the system probably automatically turned you down. When this happens, by law, they have to mail or provide you with a reason as to why your credit was denied.
But the manager said you were approved...well here's how that happens. As I previously mentioned...your app was probably automatically turned down. The Finance Manager may have called in an spoken to his rep/underwriter about your app and got them to manually overturn thus providing you with an approval.
If this is the likely scenario, you now have some clarity as to why you received the notice in the mail. Deal loaded...auto turned down, denial of credit letter generated the moment you're turned down. Finance Manager calls after the fact, gets a denial overturned, thus you having an approved deal. It happens ALL the time in the industry. There are times when my customers would receive several letters of such from lenders, often times from the very same lender that I eventually hung them with.
But going forward, just know that any time the system automatically denies you credit, you're going to get a letter explaining such. It doesn't matter if the Finance Manager had the deal overturned 10 seconds later...the fact of the matter is that the system initially turned you down and by law that letter has to be generated.
So don't sweat it, I'm pretty sure if the F&I guy said you were approved, he got you done. Disregard the letter...it's just formality.
Age is a protected class..your age doesn't matter...your age of your credit, downpayment, resources, etc matters...but not your age...that's why a 95 year old person can get a 30 year mortgage or a 5 year auto loan...