Hi Brenda,
not absolutely certain but I can't honestly see it! All charities welcome volunteers with open arms, sure they'll be glad to have you on board!! x
My mum was a helper and volunteer in a charity shop (Help the Aged) until she was 74. Even then she left of her own accord - they'd have kept her on as long as she was compos mentis and could still move.
I suppose though, being it was Help The Aged - it would have been a bit ironic to have kicked her out for being....errr...too old! That wouldn't have been very helpful would it?!!