Disability Living Allowance being replaced with PIP.?

This is purely something I just don't understand and wonder if anyone has the answer. I have been reading recently all about the governments Welfare Reform Bill. One of the things it states is that in 2013 all people of working age, 16 - 64 yrs. if eligible will lose DLA and receive PIP. However, I am sure there must be females presently receiving DLA who had worked sufficient years to get full State Pension at 60 who in 2013 will not yet be 64 so what category does this part of society come under? If you have earned your State Pension then surely you can no longer be classed as working age. Is it me or does the Dept. of Works and Pensions really confuse matters? Surely it should read those from 16 to State Pension entitlement or do they want people already classed as o.a.p's to change their status?