64 years of age.
Point of contract law: when I entered the workforce at 16 and they took social security from that first check, why doesn't the Federal Government have to honor their end of that deal and pay me full benefits at 65? Who moved those goal posts, huh? If I hadn't held up my end of the bargain I wouldn't get a great return on my self-investment, but since I held up my end of the bargain, shouldn't the other party be obligated to honor the original contract? Instead of moving the goalposts to keep and spend more of my money.