I used to have that brush. It was a good little brush that I ended up giving away.If it is one of the old stock grey boxes then I would think it is at least ten years old but your brush appears much newer than that. I would expect an old grey Simpson box to have a label similar to that shown below. Also the care leaflet inside would be different to the current one with no mention of the Isle Of Man, instead describing the brush as made in a 'rural backwater in Somerset'.
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