Shirley Greening-Jackson was told that she could not sign up to the combined internet and phone package because she was too old to understand the contract, according to the Daily Mail.
If Greening-Jackson returned, accompanied by a younger member of her family who could explain the small print to her, the application would be reconsidered.
Greening-Jackson told the paper: "I was absolutely furious. The young man said: 'Sorry, you're over 70. It's company policy. We don't sign anyone up who is over 70.'
"I have just completed a visa form to go to Russia. Last year we walked the Wall in China and here is this person saying I would not be able to understand a basic form - and it was basic. It is pure ageism.
"Somebody has decided that when you turn 70 you lose a lot of your mind. I find this is ridiculous."
The company claimed that the policy was introduced to "protect the elderly" and was discretionary.
"It is not our policy to refuse business from adult customers of any age group. However, we do ask our agents to use their discretion when dealing with older customers," said a spokeswoman.
She added that the rule was introduced last year following complaints that staff had mis-sold products.
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