What do you think was the biggest song this Summer sung by a solo female singer? Rihanna's trappy smash “Needed Me”? Ariana Grande’s sickly sweet banger “Into You”? Zara Larsson's pan-European hit “Lush Life”? Nope, nope and nope. It came from a 40-year-old bisexual vegan Australian with a nifty sideline in animal rights activism . It came from a wholly unlikely pop star: Sia.Back in July, her track “Cheap Thrills” became the first song to top the US Billboard Hot 100 sung by a woman over 40 since Madonna's "Music" in 2000. Sia stands alone as a complete anomaly in the pop world as the only female singer of her age to currently get significant chart success or airplay both in the UK and US. "But what about Madonna, Kylie, Shakira, Jennifer Lopez?" I hear you cry. Forget it – none have had comparable chart success or airplay in years. Even at 35, the relatively youthful Alicia Keys is struggling to gain traction pretty much anywhere with her bang-on trend comeback single “In Common”.So, what is it about Sia that enables her to buck this ageist curse? How is she at the top of her game so far into what has been a very long and winding career? In order to understand Sia better, we need to take it back to the beginning.Sia first emerged in the UK in the year 2000 with quirky if largely forgotten track “ Taken For Granted ” – the one that sampled the same music as used in the opening of The Apprentice. The song is most notable for its video , which establishes themes that reoccur throughout Sia's career, namely gigantic wigs, sunglasses and general paraphernalia to obstruct viewers from being able to see her face. It charted at number 10 in the UK and quickly tumbled out the chart, looking to set Sia up as a briefly interesting one hit wonder doomed to never be heard from again.This did not happen (obviously), but Sia's career would take time to re-reach the highs of the UK top 10. Her follow up single “Little Man” missed the top 75, but has endured somewhat via an amazing UK garage remix courtesy of Wookie . She noodled around a million mid-noughties Ibiza chill out compilations with her Zero 7 collaboration “Destiny ” and she broke hearts worldwide sound tracking the Six Feet Under finale with her track “ Breathe Me ”, an iconic piece of television for those that saw it (just read the YouTube comments) and a song that I still believe to be her career peak.