Henry has been training with the Arsenal squad since the MLS season ended in November and sensationally returned to Arsenal on loan for two months.
On his return debut, Henry came off the bench to score the winning goal in the Gunners' 1-0 FA Cup win over Leeds.
Koscielny was evidently impressed by Henry's work ethic in training, praising his fellow Frenchman on Arsenal's official website.
He said: "He is leading by example, we saw it on Monday night.At training, he runs everywhere. It's like he is 20 years old.
"It's thanks to players like him that we all improve. He is one of the greatest players to have played football and the squad needs to look up to him in the next two months to improve.
"Maybe he has missed the atmosphere here, at the Club and the stadium. We can see at training that he plays like if he was 20 and as if he had just broken into the first team.
"He wants to score, to help the team and to improve."
Henry, whose actual age is 34, was voted Arsenal's Greatest Player by fans and had his statue erected outside the Emirates Stadium as a part of the club's 125th anniversary celebrations.