There is no cut off date - anyone saying so is very wrong and may have a hidden agenda if they just happen to service or sell extinguishers.
They may continue in service until unsafe for use - there is no statutory lifespan, the 20 years is just advisory. Water & Foams will eventually throw off their poly linings and rust so don't go on forever, but in theory a powder in a non harsh environment will go on and on.
CO2s go on for ever as long as they are pressure tested every 10 years and cylinders that are 20, 30 & 40 years old can still be found. When pressure tested they are however, normally renovated as well and repainted in red. There is no reason to replace a CO2 extinguisher at 10 years, just service exchange it for a retested one - suppliers prefer to make you buy new as they make more money out of it.
Waters, foams and powders can also be renovated in red and before the influx of cheap far eastern extinguishers was not uncommon as cheaper than new. Renovating does not make the extinguisher EN3 compliant - it just matches the all red colour scheme.
It is ironic that in an age where we are encouraging recycling that less & less extinguishers are being recycled. Powders and CO2s were routinely refurbished in years gone by with no adverse safety or performance effects, yet now (mainly due to cheap foreign imports, the resulting price war and desperation to sell in quantity) we use more virgin steel, aluminium, brass and plastic than ever before in new extinguishers.
BSEN3 is a manufacturing standard only & has no bearing on installation and use. You can still install new extinguishers that are not red, the most common example being stainless steel/polished aluminium bodied extinguishers.
