I'm 68 now, will be 69 in November. I took mine at my "full" retirement age of 66. I did the math and figured that the break even point on 66 vs. 70 would be age 81, and who knows how long I will live.
But i didn't dare take it before 66, as there is an income penalty. After a certain income amount, I think around 17,000, they penalize you 1.00 for every 2.00 of income over the 17,000.