Nope. The worst thing you can do is to push him out of the closet. It's taken him half of his life to come to this point-- he's got to go at his own pace. While coming out isn't easy at any age, doing it later in life can come with all sorts of complications. He's worried about what friends and family will think, and adjusting to a whole new life. There are likely all sorts of fears and insecurities tied up in his decision to come out. (Check out the recent Ewan McGregor/Christopher Plummer movie Beginners for a thoughtful depiction of coming out later in life.)
The best thing you can do is to be supportive of whatever he decides to do. Keep dropping reminders that you are here to talk about whatever. Treat him as you have been. Ask about his life, relationships, whatever. He probably has reasons for why he hasn't told you yet, so let him tell you in his own time. The fact that you have history together (maybe romantic?) might account for his hesitation. All you can do is continue to be a good friend, a shoulder to cry on, and all the rest. If he still doesn't tell you after some time has passed, put on a Matthew McConaughey movie, wait until the inevitable shirtless scene, and go, "Is it getting hot in here or what?? Right???"
Why does he have to come out? He can bring a friend or partner in there. He doesn’t care to share his life with the world…, don’t make him.