You still have to be age 55 regardless of your factor to be eligible for retirement. In may case I was 54 with 33 years service (87 factor) and got layed-off. How that screwed me was I could not take the severance package as a lump sum and direct it to my retirement fund. Instead I had to take the continuance package which does not allow you to retire.
I know some of you will say that I was lucky to get anything at all, but think about it. I was with the company for 33 years and all they would have to do is wait 1 more year (a little bit less actually given I was to turn 55 in 2018) before I could have retired. But like many other posts have stated, I was not willing to conform and made my opinions known to senior management (although respectful). It cost me my retirement. I am now having to work a minimum of 10 more years and put my 2nd job income towards my retirement fund.