If someone is in their 70's and their sole income is from Social Security and Pension totalling just under 16,000 do they need to file federal taxes?

Generally not, but... in order to receive the stimulus payments that the government will be sending out starting in May (also known as the 2007 tax "rebate"), one must file a tax return for 2007, even if no tax is due. This person can submit a form 1040A - the IRS has some helpful info on this here:
Economic Stimulus Payments Information Center

Click on the "Especially for Social Security Recipients" link.