I'm equally interested in how Althea Gibson would have done if she played past age 31.
Gibson won the final four Majors she played from 1957-1958, winning Wimbledon and the U.S. National Championships twice, dropping only one set across the four finals.
That final U.S. National Championships title came over Darlene Hard just after Gibson had just turned 31 on August 25th. Gibson ended her career 10-0 against Hard.
After that, due to the absence of money in amateur tennis, Gibson turned pro and played exhibition tennis matches before Harlem Globetrotters games, then joined the LPGA to try to make more money.
With Gibson gone, Hard (3), Maria Bueno (6), and Margaret Court (9) won the lion's share of women's Majors from 1959-1964 when I think Gibson would have been very competitive (up to age 36ish) due to lack of mileage. As noted, she was 10-0 against Hard, and she was also 3-0 against Bueno, with all three matches in 1958, just before Bueno won Wimbledon and the U.S. National Championships in 1959.
Unfortunately, Gibson and Court never played against each other.