I have used air and HeO2 stored in industrial steel gas cylinders that was over 5 years old. Oxygen levels analyzed exactly as the cylinders were labeled. Keep in mind that industrial cylinders in the US are on a 10 year hydro cycle.
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hope you mean 210 bar, you aren't going to get very far on 210 psi
If there is no moisture in the cylinder, then there is no time limit for an air or Nitrox fill.
Of course, you can't tell whether or not there is moisture in the cylinder without draining the tank and removing the valve for a peek inside.
So always assume that you cylinder is wet inside, to some degree.
In aluminum tanks, the air will last forever. But the oxygen and moisture can cause severe corrosion of the cylinder. That's why tanks need to be visually inspected (VIP=visual inspection program). Most people assume the VIP is annual, but the schedule actually depends on how often the tanks are used. Tanks should get a VIP at least once annually, but a VIP every 3-4 months is more appropriate for a busy dive shop.
Steel tanks are a different story. The formation of steel rust actually consumes the oxygen in the cylinder, and you could end up with a hypoxic gas. There is one recorded scuba death from this problem. Again, this is why the VIP is so important.
In summary, the evidence-based recommendation are:
-Make sure that your tank gets a VIP at least annually
-If you tank has been sitting for more than a year, check the O2 with an oxygen analyzer before use, and then get your tank inspected after the dive
-If a steel tank sits for more than 3 months, check the O2 with an oxygen analyzer before use