Thanks for the answers so far, which led me to some more answers, and left me with a lot of calculations to ponder.
I've asked a few people in the non-virtual world, including some of them already getting benefits, and nobody knew the right answers. I assume AARP has this right:
It starts with Social Security examining your earnings history — with an emphasis on the money you earned during your
35 highest-paid years.
That means that if you worked 40 years, Social Security would use your highest-paid 35 years in its calculations and ignore the other five. If you worked only 25 years, Social Security would consider those 25 years and factor in an additional 10 years as zeros.
The calculation of your PIA is subject to a set of percentages derived from the AIME, known as
"bend points." Essentially, the PIA is the sum of three parts of your AIME. For instance: In 2017, retirees get 90 percent of the first $885 of the AIME, plus 32 percent of any AIME dollars between $885 and $5,336, plus 15 percent of AIME amounts above $5,336.
So, that means that taking a smaller wage for the last ten years of work would knock me down some, but not as bad as if they only looked at the last years, as some people said.
Fidelity says you can start at 62, but the benefit is reduced by about 30% if you start at 62, and a bit less until you get to 100% at FRA (full retirement age, 67 for me). Then, you also get 8% more each year up to 70 if you wait even longer, which sounds like a square deal.
I still don't understand the penalty for working while you receive benefit, or really anything about medicare.