No problem. Spoiler alert: the news is bad.
Notice that the tanks are stamped DOT – 6498. That number is the special permit (used to be called exemption) that those tanks were manufactured under. A quick google shows that they were made by Luxfer.
Luxfer made tanks for most all of the scuba companies. US divers, aqualung, Dacor and others. If it’s a scuba company branded tank, it’s about 95+ percent that they were made by Luxfer.
Here’s a link that documents the 6498 tanks being Luxfer:
https://scubaengineer.com/documents/luxfer_qa_south asia technical seminars 2-02.pdf
And yes: their born on dates are long before 1990, so you are assured that they are made of 6351 aluminum.
ETA: yeah, next time I’m just gonna wait slightly longer.
@lexvil covered everything you need to know.
ETA2: well, maybe one thing he didn’t cover. These tanks are not a catastrophe. They are not a direct and serious danger if they are handled correctly according to the information outlined above. However, there is a slight but real risk that the tank will rupture. And therefore it is practically impossible to get those tanks filled. Dive shops say it’s because of that risk that they refuse to fill them. Personally, I feel it’s because it gave them an excuse to sell people new scuba tanks – a feeling that has only been reinforced by some dive shops refusing to fill any aluminum scuba tank more than 20 years old, with zero evidence of increased risk for those tanks.
In any case, it’s very much a case of their compressor, their rules. Personally, I fill my own tanks and I have a half dozen or so of aluminum tanks made out of 6351 aluminum. However, I am meticulous with those tanks: they get hydroed every five years, with a VE test performed every year. I can borrow a VE tester so it doesn’t cost me anything. If it did, I would scrap them. Not worth the cost when a tank made out of 6061 aluminum is fairly cheap to buy.
