As she turns 40, Venus Williams continues to transcend tennis. She's still inspiring millions of girls - and also boys - around the world... just not necessarily to pick up a racquet and play tennis.

I'm amazed that Venus is still playing on the WTA Tour at the age of 40, especially when you consider she has also been dealing with Sjögren's syndrome, an auto-immune disease that can sap your energy. That significant birthday is the occasion to pause and recognise that Venus's impact goes way beyond the tennis court. Her greatest impact has been socially, politically and culturally. As well as a champion tennis player, she's also an iconic figure and a leader in the fight for equality.

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For all that she has accomplished in the sport - including winning seven Grand Slam singles titles and holding the WTA World No.1 ranking - I don't think she has actually inspired that many people to play tennis like her.

She's just so tall, long and amazing that it's hard to relate to exactly how she plays tennis. You can admire her tennis but it's difficult to say: "I'm going to learn to play just like that." But she continues to inspire kids to try tennis, or to get better at whatever else they are doing. That's the beauty of Venus, that this is about more than just tennis.

Venus has been a political and social leader. She has been very vocal about fighting for equality. While Venus wasn't the first Black athlete in tennis, she was certainly still a trailblazer and 'an anomaly'. She has carried that baton for equality for years, along with her younger sister Serena.

I'm sure she has motivated millions of girls of color in the United States, and also around the world, to follow their dreams, whether in tennis or any other sport or industry. They're going to be looking at Venus and saying to themselves: "If she can do it, I can too." She also played a major role in persuading Wimbledon to pay equal prize money to women - the final Slam to do so.

I used to think that Venus would retire sometime around her 25th birthday. I remember her saying as a young woman that she would quit tennis in her mid-20s and do something else. Back then, the prospect of Venus still playing on the WTA Tour at aged 40 was just unimaginable.

So what has kept her going all these years? Clearly, she just loves tennis. She loves getting out there and doing her thing, and competing, and she has found a way of dealing with Sjögren's syndrome. I would think she has also realised that maybe, whatever she does next, she won't be as good at it as she is at playing tennis, that she won't necessarily be the best in the world at something else.

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Venus has reached the very top in tennis but even though she is now ranked outside the Top 50, she wants to keep on competing, and why shouldn't she if it's making her happy? When your ranking slides, it can be a struggle as you're not seeded, so you don't have any protection in the draws. But Venus still seems to be hugely motivated to compete at the highest level, 20 years after she won her first singles major at the 2000 Wimbledon Championships.

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I'm sure it helps Venus and Serena that the other sister is still playing. They're still feeding off each other and inspiring each other. While the sisters have their own lives and own careers, there's such a strong connection there.

Some have wondered whether Venus might have found it hard watching her younger sister win more titles than her. But I don't think that older sisters tend to think like that. As the older sister, you're always looking out for the younger one. Venus is only going to wish Serena well. She would be totally thrilled if Serena wins another major or two. All she cares about is that a Williams sister wins a title and then it's kind of like a family trophy.

Venus at 40: Magic moments