If you do that, the working old folks won't be supporting those already on Social Security and they will just stay home and vote for more benefits for themselves to be paid for by the young non-voters.

And they keep living longer than they used to!  When FDR invented Social Security, almost no one  lived long enough to collect it!  That's why "65" was selected! 

"When Social Security was created in 1935, the average life expectancy was under the retirement age of 65. This fact ensured that comparatively few people would receive Social Security benefit." 

Now look how it is!