If you're like most older players, you've gradually lost some flexibility over the years, and that can often show up in an inability to make a full turn behind the ball. Needless to say, it's a good bet that your distance has suffered because of this common problem. To get some of that old turning ability back, try releasing your left knee during your backswing. Let the momentum of your takeaway pull the left knee back so that if you were standing on a clockface, your kneecap would point at 1:00 at the top of your swing. This prevents the knee from dipping and frees your upper body to make a full turn.
On the downswing, start with your knee at 1:00, but allow it to gradually open to roughly 12:00 as you come down to impact. But don't rush this move—if you open the knee too quickly, your entire left side may spin out and ruin the proper sequence of body movements down to the ball.