I ran into this just the other day when I went back to U-Haul to have another tank refilled. They wouldn't fill it because the date on the tank was 07/10 and the U-Haul guy said they are only good for 10 years and I would have to go exchange mine. Are they ever re-certified? I went to Walmart and exchanged it, but the tank they gave me was even older - dated 06/07. So now presumably I'll have to exchange that one too when it runs out.
I have a couple 40lb tanks I use with salamander heaters. A few years ago Tractor supply wouldn't fill one because it was out of date. I ran up to Kokomo and had it re-certified at Amerigas(was around $35 for cert and a fill if I remember correctly). The re-certify does not last as long as on a new tank, but I can't remember right now how long.