For this new subset analysis on healthy aging, those who met the age criteria were < 60 years old in 1984.
"We included 48,762 NHS participants aged <60 y in 1984. "

But "In its entirety, the WHI enrolled more than 160,000 postmenopausal women aged 50–79 years (at time of study enrollment) over 15 years, making it one of the largest U.S. prevention studies of its kind, with a budget of $625 million."