Research compiled from figures taken from the main UK broadcasters found just 18% of presenters over 50 are women. The figures also reveal only 7% of the total TV workforce (on and off screen) are women over the age of 50.
Harman, told Radio 4's Today programme, there needs to be a culture change in the TV industry.
"When it comes to men, they can get better with age - their grey hair denotes wisdom, experience and authority," Harman said.
"But for women they get worse with age. They have to start looking younger and younger, many, many years below their age. And then when they get to about 50 somehow the viewers need to be protected from them, and I don't think that is acceptable."
She added: "I don't think women in the country think that just when they are past 50 they have to be airbrushed off our screens."
Last year former presenter of BBC's Countryfile, Miriam O'Reilly, won an age discrimination case after the broadcaster dropped her from the programme.
After the case, O'Reilly said: "Right from the get-go, there was no interest from HR in my case.
"But, as a journalist, I felt I simply couldn't let it go. The BBC never thought I would go to a tribunal; when it finally realised I was serious, it tried to settle, but I refused.
"Signing anything meant accepting gagging orders, and someone needed to speak out. I felt that being free to do this allowed me to be as damaging to it as I could."
Last year Harman set up the Older Women's Commission after finding it "unacceptable" that women in television who were entering their fifties were on "borrowed time".
Senior executives at the BBC, ITV, ITN, Channel 4, Channel 5 and Sky will today meet members of the Older Women's Commission to discuss how to end discrimination.