James Hong. 
Guy: “I’m looking for Jack Reacher.”
Hong: That’s me.
Guy: I don’t get it. I thought you’d be a tall dangerous looking white guy.
Hong: YOU WERE NOT PUT UPON THIS EARTH TO ‘GET IT’, WHITE BOY.
Guy: They told me you were an American.
Hong: I was born in Minneapolis, you racist fuck.
Yeah, he’s no youngster. In story, his mother was a young teenager during WWII, and Reacher was badly wounded in the Beirut Marine barracks bombing in 1983, so the birth year that wiki offers of 1960 seems about right.
They’ll adjust that for the show, I’d think, to make him an Iraq/Afghanistan vet.
Well, lots and lots of heroes have to have their back stories updated to account for the times.
Indeed. I don’t actually care that much that whoever plays Reacher is appropriately sized even, it has just got to be someone who can play the role of knight-errant convincingly.
The guy who plays Amos on the Expanse would be a good fit. Nicely terse, big enough. Probably a little too busy.
Nikolaj Coster-Waldau is 48, about Reacher’s age through many of the books, and he’s 6’2 or 6’3. He’s already pretty large, around 200 lbs. Give him a trainer, and he could easily be 220.
Have a look at him in this shot - imagine him without that mustache and shorter hair, and he’s a pretty good Reacher.
Come to think of it, an even better fit would be Tom Hopper, the guy who played Dickon Tarley. He’s 6’5" and 230 lbs, and would be just about perfect.