From the best fittings website.(this seems to match the markings)
Design Life 15 Years,
15 Year Design Life is typical of the vast majority of composite cylinders available for use in the UK/EU.
5 Year cylinder hydro-static test cycle from date of manufacture.
Cylinder Decommission Date:
15 Years from Manufacture Date detailed on the cylinder.
Decommission date refers to the last date that the cylinder can be filled at a commercial fill station. You can safely continue to use the cylinder after this date until the air is depleted, it just cannot be commercially re-filled.