Medicare Prescription Drug Flexibility for Seniors Act of 2005 - Amends title XVIII (Medicare) of the Social Security Act to: (1) specify extended periods of initial enrollment for the Medicare prescription drug benefit without incurring a late enrollment penalty; (2) permit Medicare beneficiaries enrolled under prescription drug plans that change their formularies to enroll under other plans; and (3) apply a civil monetary penalty to employers who provide false statements with respect to offering Medicare creditable prescription drug coverage.