'Golden Sisters' Mary -- Gimme a Sponge Bath ... I Wanna Sell Burgers

Take ex Carl's Jr. hotties Kate Upton, Audrina Patridge, and Charlotte McKinney ... and their combined age would still be younger than Mary Bartnicki -- who's gunning to be the next burger babe.

Mary -- 1/3 of the 'Golden Sisters' -- is 83 years old and throwing her Depends in the ring to be the new face of Carl's Jr. She's serious and even put together a sexy car wash vid to prove she can still work it, by which we mean ... chew a burger.

Fun Fact: Carl's Jr. gives senior citizens a 10% discount.