The Take That singer and fellow judges Louis Walsh, Sharon Osbourne and Nicole Scherzinger were so impressed with ten-piece group The Nostalgics - which includes pensioner Bill and a woman who had just had a pacemaker fitted - that they have put them through to boot camp.
According To The Sun, Gary said after the band's rendition of Katy Perry's 'Firework': "I want to know the name of the woman on the organ. Is it Elton? Oh, it's Betty. I love Betty on the organ. Betty, you got everybody up. Well done."
And Louis added: "I loved everything about it."
A source said: "The X Factor's had contestants from all different walks of life and of many different ages but Bill is definitely the oldest.
"I'm sure we've never had anyone who had a pacemaker fitted days before auditioning."
But the insider suggested the group might be in for a bit of a "culture shock" when they get to boot camp.
"That stage of the competition is traditionally the most rowdy and raucous, with all-night boozing, music and bed-hopping. The producers might have to put The Nostalgics into a different part of the hotel. Having said that, if their audition is anything to go by, they may well want to get involved in the action and have a good time."