Any income you receive from Canada Pension Plan (T4AP) Old Age Security (T4AOAS) and private pension plans (T4A) is taxable income. Only income from the Guaranteed Income Supplement in Box 21 of your T4AOAS slip is "not taxable".

However, as a senior you have higher personal amounts, therefore you are able to receive more income before it does become taxable. (It could be close to $20,000 depending on your personal situation).