Steve Kerr can't even physically COACH a team right now, he ain't doing shyt at the rec.
But if we brought him back to health, even at his current age, he'd clearly look like he was on another level than everyone else. He wouldn't have the stamina/speed to keep up if it's a legitimate game (college players, high school players, in shape cats) but from a skill perspective you'd be able to tell who was a former professional.
When I was in high school my coach was a fringe NBA player in the '80s (was an McDonald's All American, played in the ACC, didn't have much of a career in the league but did make it there) and was probably in his 40s when I was in high school and clearly didn't do any type of regular exercise or anything (and was a known semi-alcoholic on top o that), but when he randomly played in a scrimmage with us out there he was just shredding the defense with the most amazing court vision I ever saw and was just hitting random jump shots from all over the court. We were competing for a state title at the time and had three or four dudes that ended up D1, and our coach wouldn't really run up and down the floor with us, but whenever he got the ball it was just clear there was levels to that shyt, even at that age.
Steve Kerr would be a notch even above that.