In the 1970s, there were 13 boys for every one girl who scored exceptionally high on the SAT math test as a child. By the 1990s, the ratio had decreased to three boys for every one girl.
This stat doesn't support the claim that the gap at high levels of math have been shrinking. In the timeframe discussed, the SAT was made much easier. What an 700+ math score in 1970 means is a much higher mathematical ability than a 700+ in the 1990s. It's apples and oranges. I would like the claim to be true, but the quoted fact doesn't support it.