The canonical source of unemployment numbers in the United States is the Bureau of Labor Statistics, which says that the unemployment rate for women is currently 4.0%. It may be worth noting that in October 2017, the unemployment rate for women was 3.9%. However, that was also during the Donald Trump administration.
To see unemployment rates over time, one possibility is to use the St. Louis Federal Reserve Bank's graph, which says that in December 2017, the rate was 4.0% and that the last time the rate was lower before Trump was president was in December of 2000, when it was 3.8%. I'd call that seventeen years, although one could argue that it covers an eighteen year period because 2000 to 2017 involves eighteen different years.
U.S. Bureau of Labor Statistics, Unemployment Rate: Women [LNS14000002], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/LNS14000002, January 20, 2018.
A more accurate way to state things would be that unemployment among women is lower than it was at any time under the George W. Bush and Barack Obama administrations. Or women's unemployment as of December 2017 was tied for the fourth lowest it's been in the last sixty years (October 2017 was tied for the second lowest with October of 2000, Only December of 2000 was lower). Women's unemployment was not as low or lower at any time in the Kennedy through George H. W. Bush administrations. It was lower in the Harry S Truman and Dwight Eisenhower administrations, more than sixty years ago. The St. Louis Fed doesn't go further back.
I'll leave it up to you whether that was more true than you expected or less precise than he should have made it. Or both.