No retirement, pension or profit sharing plan, qualified for tax exemption purposes under present or future Acts of Congress, or any trusts, insurance and annuity contracts constituting a part thereof, shall be construed as violating the rule or law against perpetuities, or any rule or law against restraints on alienation; provided the power of alienation or the vesting of the interest of any person in such plan, trust or contract shall not be suspended for a longer period than the duration of the lives of the designated beneficiaries of such particular interest, in being at the time of designation, plus twenty-one (21) years.