PRINCETON, N.J. — The first members of the huge baby-boom generation in the U.S. have reached retirement age in recent years, and these older boomers are retiring in large numbers, just as Americans in their mid- to late 60s did a few years earlier. While about eight in 10 boomers in their early 50s are in the workforce, the percentage employed drops to about 50% for boomers who are 60, and the proportion accelerates downward with each year of age thereafter. Only about a third of those aged 67 and 68 — the oldest boomers — are still working in some capacity.