Serena and Venus Williams have reached the singles semifinals at Wimbledon, which is a remarkable event, for siblings.

It gets more remarkable.

This is the 11th time the two of them have reached the semifinals at a grand-slam tournament. On the previous 10 occasions, one of them went on to win the championship, contributing to their haul of 28 major championships (21 for Serena).

They have met in a major final eight times, most recently at Wimbledon in 2009, with Serena holding a 6-2 lead.

And then we get to the longevity marks, which the sisters are staking a claim to.

–When Serena won at Wimbledon last year, she become the oldest woman in the open era (since 1968) to win a major, at 33 years and 9 months, pushing Martina Navratilova (33 years, 8 months) out of the record book.

–If she wins this Wimbledon tournament, Venus, 36 as of June 17, would become the oldest woman to win a major, eclipsing her sister.

–Venus is the oldest woman to reach a major semifinal since Navratilova did at age 37 in 1994.

–Every 24 hours, Serena becomes, by one more day, the oldest woman to hold the No. 1 ranking.

–It is not as if the sisters were late bloomers who saved some wear and tear on their bodies. Venus won her first major at age 20 (Wimbledon, 2000); Serena won her first major (1999 U.S. Open) just shy of her 18 birthday.

The sisters, along with Navratilova a generation ago, are pushing back the boundaries of what is possible on the court for a woman late in a career.

A sample (from nearly three years ago) of what we thought were geriatric slam winners, in previous decades: Virginia Wade was 10 days short of 32 when she won her last major; Billie Jean King was 31 years, 7 months when she won her last slam; Chris Evert was 31 and 5.

The Williams’s run to the semis is not some fluky thing. Venus is ranked No. 8 in the world as she overcomes the ravages of an energy-sapping disease. Serena is, of course, No. 1 and has been for 177 consecutive weeks, nine short of Steffi Graf‘s record.

Only two men have won major events at an age older than Serena has: Andres Gimeno, who was 34 years, 10 months, when he won the 1972 French Open, and the remarkable Australian Ken Rosewall, who won three majors in the open era at an age older than anyone else, male or female, the last coming at the age of 37 years and 2 months at the 1972 Australian Open.

Hmm … 37 and 2?

Venus could break Rosewall’s record if she won the 2017 U.S. Open. Serena could eclipse him if she won the 2019 Australian.

Less unlikely by the day.