Deontay Wilder's Fighting Til He's At Least 40, Says Fiancee Telli Swift

Deontay Wilder's rich, famous and a heavyweight champ ... something he's not: anywhere near done knockin' dudes out -- 'cause his fiancee tells TMZ Sports he plans to fight til he's 40!!!

We talked to Telli Swift earlier this week in L.A. ... and with Wilder's 34th birthday coming up next month, we asked how much longer the Bronze Bomber plans to fight.

"Deontay's gonna go until he wants to stop. He says 40, but who knows. If his body allows him to."

"At least [40]."

FYI, Wilder's widely regarded as the hardest puncher in the world ... and has a record of 41-0-1 with 40 knockouts.

Telli also cleared up her man's immediate fighting future.

Deontay's supposed to rematch Luis "King Kong" Ortiz later this year ... but the fight hasn't officially been announced, leading to speculation it ain't gonna happen.

Swift says they're wrong ... 'cause it's 100% goin' down.

"It's happening. It's happening in November."