Had some 20+ years old Kodachrome developed.
The development voucher coming with it was still valid so I used it
Sent it to Stuttgart, Germany, developped film came back from Switzerland with a remark from Kodak labs that image quality may have been compromised due to excessive storage time
What a service!
Actually, image quality was still good. Nothing a little bit of PP couldn't fix. However, there have been spots where light managed to travel into the roll over the years.
So, definitely give it a try!