The way I look at it, FRA is actually 70 for everyone. If you take it earlier, you get less.
When should you take it? That depends on several factors including your health/life expectancy, your financial needs and your spouse's financial needs. Generally, if you are not expecting to live long, take it as soon as you can (morbid but realistic). If you don't need the money delay taking it (~8% gain per year is pretty darn good!). If your spouse is going to be dependent on your SS after you pass you may also want to consider delaying (this one is much more complicated).
Personally, I will not decide when to take SS until I hit minimum age. Then I will assess my current health and financial needs regularly, probably annually, and decide then. Right now I am healthy and expect to live into my mid to late 90s but who knows what will happen in the next 5, 10, or 15 years?
No one should delay past 70 because after that, your benefits stop increasing.
On the macro level, who knows what will happen to the SS benefit structure either? I will keep an eye on that as well.