Film lecturer Drew Cummings says he was told he was too old to compete when he turned up for an audition in Miami Beach in November.
"
If... I become the poster child for baby boomers and age discrimination rights, that's fine with me
"
Drew Cummings
The show - which begins its second season on Tuesday - has a strict age band for contestants of 16 to 24 and reserves the right to disqualify them for any reason.
But Mr Cummings argues that these rules contravene American laws banning age discrimination.
"Age discrimination runs rampant in the entertainment industry and corporate America," said Mr Cummings.
"It's time that someone did something about it."
Mr Cummings, who works in television as well as teaching, quotes record industry statistics showing that 55% of all record sales and 65% of all concert tour revenues are dominated by performers over the age of 40.
The 50-year-old professor says he is happy to become a "poster child" for the rights of the post-war generation and other ageing people.
His lawyer, Frederick Kramer, said talent was not an issue in the producers' decision to exclude his client from auditions for the British-inspired contest, in which more than 70,000 people across the US took part.
"Mr Cummings was summarily denied the right to compete and he was discriminated against solely because of his age, not his ability as a singer," the lawyer said.