When Billie Jean King left college in 1964, she had a purpose. Within a few years, she had become the top-ranked tennis professional in the world. Over a trailblazing career, she won 39 championships, a Presidential Medal of Freedom and a congressional Medal of Honor – all while pushing publicly for gender and pay equality.

Last year, she finally returned to finish the degree in history she started more than six decades ago. On Monday, she graduated, at 82 years old.

“It is a privilege for me to be here as a member of your graduating class,” King said at her commencement. “Yeah baby, only 61 years!”

King recalled growing up in a working-class family, the daughter of a firefighter father and homemaker mother.

“Like so many of my fellow graduates, I am the first member of my immediate family to graduate college, like many of you,” King said.

She chose Cal State Los Angeles, then known as Los Angeles State College, because the tennis coach, Scotty Deeds, trained men and women together. He said it would help give her the level of competition she needed to excel.

“Their approach to winning in tennis was revolutionary at the time,” King said of Deeds and the women’s coach Dr Joan Johnson. “Even today most collegiate D-1 and D-2 tennis teams do not have the women and men practice together. Scotty and Dr Johnson had it right and they took the extra step for their student athletes.”

King distinguished herself as a tennis champ in college, winning Wimbledon doubles while enrolled. King was 18 and her partner, Karen Hantze, was 17, making them the youngest team to win at the time.

But King told the crowd that her true motivation since childhood had been to fight discrimination, a calling she first remembered feeling at age 12, when she realized that virtually everyone at the tennis clubs where she trained was white.

“I asked myself, where is everybody else?” King said. “From that day forward, I committed my life to equality and inclusion for all. Tennis is a global sport and it became my platform, but equality was my dream – to make the world a better place.”

She added: “We can never understand inclusion unless we’ve been excluded.”

King, one of the first openly gay professional athletes, founded the Women’s Tennis Association in 1973 and successfully campaigned to get the US Open to pay equal purses at the US Open. That same year, she defeated Bobby Riggs in a historic match billed “The Battle of the Sexes” – a feat later dramatized in a Hollywood film staring Emma Stone and Steve Carell.

King ended her speech with words of advice for her fellow graduates.

“Have fun,” King said. “Be fearless. And make history.”