LONDON, UK - Having played professionally until she was 40, WTA legend Billie Jean King knows a few things about what it takes to keep up with the younger generation on court.

"As you get older you have to work harder," the 12-time Grand Slam champion said during a roundtable interview this week in London, where she had just announced changes to the format of Fed Cup. "Smarter and harder - you gotta be intense, but maybe not quite as long. But you've got to workout, you've got to watch your nutrition more than ever because you tend to thicken as you get older, it's a nightmare. But if you love to play that's the price you're willing to pay, that's why I made that decision."

As such, King has some advice for 37-year-old Serena Williams as the former World No.1 aims once more to capture her 24th major. Williams - who, it must be remembered, only gave birth to daughter Olympia 22 months ago - has been repeatedly set back by injuries in 2019, in particular a troublesome knee; she has retired or withdrawn from three of her five tournaments this season, and is coming off a third-round loss at Roland Garros to Sofia Kenin.

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While acknowledging this, King nonetheless said: "Ideally I would like her to play matches before she gets to Wimbledon. In the old days she could kind of get through and then get going by the second week, but I think when you're older that doesn't work that way."

But the larger picture, to King, is of a formidable champion stretched in many directions, including her own Billie Jean King Leadership Initiative. "She's got a baby, she's trying to help gender equity, particularly women of color," she pointed out admiringly. "But it makes it much harder. I would like her to put everything else aside, because she's got people working on those things. I wish she would just make a commitment for the next year-and-a-half to two years and say, I'm going to absolutely focus on what's necessary for my tennis, so when I look in the mirror when I'm older then I can go back in my mind and know I gave it everything I had."

Ultimately, though, Williams's priorities are her own choice, said King: "If she's happy doing it this way, then that's fine. It's whatever makes her happy - it's not about us."

Serena Williams practises ahead of Wimbledon 2019 (Getty)

After all, King knows a few things about being stretched in multiple directions at the expense of her on-court numbers. When she was playing, she said, she had no focus on her Slam count whatsoever. "What we were concerned with was trying to get professional tennis off the ground... All I cared about was making our sport for everyone and having prize money equality and having a place to compete and be appreciated."

Indeed, King believes the historical context around Margaret Court's record of 24 Grand Slam trophies is insufficiently understood. Asked whether too much is made of the number 24, King responded emphatically: "I sure do!" She pointed out that many players, such as herself, Chris Evert and Martina Navratilova, had passed up entering many major tournaments during their primes. "You gotta remember we didn't play the Australian Open for many, many years - we played the Virginia Slims in San Francisco. And we also played Team Tennis during the French Open. I think those two [Evert and Navratilova] would have had a lot more than 24, quite frankly."

Ashleigh Barty practises ahead of Wimbledon 2019 (Getty)

One player whose Slam count is only just beginning is brand new World No.1 and Roland Garros champion Ashleigh Barty, whose classic technique delights King immensely. "You know what's happening to tennis? It's going back to an all-round sport!" she said. "You see the way she plays - it's like the old days. She's got a sliced backhand, she can hit it, she goes to the net, she can stay back. I think it's great."

The Australian's decision to take a hiatus from the game also drew praise from the six-time Wimbledon champion: "I think playing cricket for a year-and-a-half gave her a tremendous perspective on herself and what she really wanted out of life... [It shows] there's no one set way, it's definitely not linear. Everybody has their own journey and there are many journeys to becoming a winner."

Read more: Wimbledon 2019: 'She's not following anyone else's path' - Coaches, legends and players on Ash Barty's big breakthrough

Though King has no official pick to win Wimbledon - "I think it's wide open" - Barty was the only name that came to her lips when mulling the question over. "She's got an all-court game, she's gonna be one of the best players on grass."

Johanna Konta practises ahead of Wimbledon 2019 (Getty)

As for British No.1 Johanna Konta, whose own career-best clay season was halted 7-5, 7-6(2) in the semifinals of Roland Garros by 19-year-old Marketa Vondrousova - after Konta had led by a break in both sets - King had no truck with the suggestion that it had been a missed opportunity.

"She did great, the best she's ever done, so use it!" she declared. "Don't think just because you didn't win it, so what? Why didn't I win it? What could I have done better in that much? How can I keep using what I learned about myself - what did I do well, where did I break down a little bit? 

"It's hard to finish and some players never learn how to. They get close, but not quite. If I was a player and that happened to me I'd think, I gotta make this happen. Am I trying for too much or not enough? That's another very big question."

Embracing the big questions is still what King, at the age of 75, thrives on - and the answers Williams, Barty, Konta and the rest of the field come up with to their own individual circumstances are what will make Wimbledon such an intriguing competition this year.