6:43 AM PT -- Kraft's reps just issued a statement saying he is actually NOT the father of his GF's baby.
"While Robert Kraft is not the biological father, he is thrilled with Ricki’s blessing of having a healthy child."
Age ain't nothin' but a number for Robert Kraft ... the 76-year-old Patriots owner's 38-year-old girlfriend has reportedly given birth to a secret baby -- and signs point to Kraft being the daddy.
Kraft's GF, Ricki Noel Lander, gave birth to the baby in 2017, according to Page Six ... but kept everything from the pregnancy to the delivery out of the public eye.
When reached for comment, the Patriots told Page Six, "This is a private matter."
Kraft -- who already has 4 adult sons -- reportedly bought Lander a home in Los Angeles and is taking care of both Ricki and the baby.
We've seen them out and about for years -- most recently back in December when they were strolling around Beverly Hills together and Kraft bragged that he was with a "lovely lady."
Sooooo ... congrats!?