Subject to the limitations of paragraph (6), premiums paid during the taxable year by a taxpayer before he attains the age of 65 for insurance covering medical care (within the meaning of subparagraphs (A), (B), and (C) of paragraph (1)) for the taxpayer, his spouse, or a dependent after the taxpayer attains the age of 65 shall be treated as expenses paid during the taxable year for insurance which constitutes medical care if premiums for such insurance are payable (on a level payment basis) under the contract for a period of 10 years or more or until the year in which the taxpayer attains the age of 65 (but in no case for a period of less than 5 years).