Rick Perry has called into question Mitt Romney's about-face on gay rights.

During an appearance on Fox News' O'Reilly Factor, Perry told host Bill O'Reilly that he's concerned about Romney changing his mind on issues.

When O'Reilly asked: “Do you respect the evolution that the guy might have gone through?” Texas Governor Perry answered: “How do you change at the age of 50 or 60 positions on life, positions on guns, positions on traditional marriage. I mean, those aren't minor issues, Bill. So, to change those at age of 50 or 60 tells you all you need to know about that.” (The video is embedded in the right panel of this page.)

During Romney's tenure as governor of Massachusetts, the state's top court legalized gay marriage. Romney at first attempted to strike a more moderate tone on gay rights by backing civil unions for gay couples. He would later reverse himself, backing a constitutional amendment that would have overruled the court's decision and make no provisions for civil unions. And in campaigning for the U.S. Senate in 1994, Romney claimed he would be a stronger advocate for gay rights than then-Senator Edward M. Kennedy.

“We must make equality for gays and lesbians a mainstream concern,” Romney wrote in a letter to gay GOP group Log Cabin Club of Massachusetts.

(Related: Mitt Romney's gay rights flip-flop slammed by Obama strategist David Axelrod.)