NOT ALL THAT FLEXIBLE?
Some young players can keep the left heel flat and coil fully. But age isn’t as crucial as flexibility. You might need to let your heel come up. Letting your left heel come off the ground during your backswing can help you make a full turn. I’ve always let my heel rise because my trunk is not as flexible as some golfers’, and I have a long backswing. Other players can keep the heel on the ground and complete a fully coiled shoulder rotation—either way works.
If you’re less flexible in your hips and lower back, the heel needs to come up, because of the hip rotation required to make a full backswing. The longer the backswing—driver versus pitching wedge, for example—the more the heel lifts. Provided you stay in balance and retain the tight coil of the backswing, it can go as high as necessary. Too much lifting results in an over-rotation of the hips and loss of a true coil. You don’t want to overdo it, and it’s critical you replant the heel in its original position during the transition to the downswing. That’s a function of the hip turn reversing its rotation. At the finish, the heel should be back where it started.