Tom Brady Reveals 15-Year-Old Son, Jack, Nearly As Tall As Him Now

G.O.A.T. blood apparently runs thick in the Tom Brady family ... 'cause the greatest quarterback of all time just revealed his 15-year-old son is nearly as big as he is now!!!

The 6-foot-4 Brady shared the eyebrow-raising update in an Instagram post on Thursday afternoon ... showing Jack -- his son with Bridget Moynahan -- is only a couple inches away from Pops now.

"Not Yet Kid!!!" Brady said in a caption on the post. "I'm still here."

The 44-year-old added a bunch of laughing emojis and a few hearts as well.

Of course, while Tom still might have the height and the athleticism edge over Jack these days -- it doesn't seem like it'll be long before the teen can claim both titles from Dad.

The younger Brady is very much into sports -- he actually plays QB for his high school football team -- and he even showed he's got an arm at a Buccaneers practice late last year.

Tom, though, said in an interview with ESPN last week that he wouldn't "choose" for his son to continue down the quarterback path due to the "crazy" and "unfair" expectations that would be placed on him.