Love & Hip Hop Star Sincere -- Karlie Redd Will Make Great Gran

YOU COULDN'T PAY ME

Karlie Redd must be gunning for fans of a particular porn fetish -- at least according to another 'Love & Hip Hop' star who says she's just too damn old to be having sex on camera.

Sincere Show ... from 'L&HH Hollywood' ... has heard all about Karlie's offer to get down and dirty for Vivid. She hasn't decided yet if she's gonna do it -- so he decided to give Karlie some advice.

Sincere's take is no-holds barred, hysterical ... and a little ageist. Karlie's official age is -- she doesn't have one. 'L&HH' fans estimate her range to be from 37 to 49.

Karlie won't like what Sincere has to say -- and neither will fans of GILFs.