I received a nice tip from a teaching pro at allexperts.com (Eddie Kilthau).  It is called "palm up palm down drill.

For a rightie, hold your left hand at shoulder level with hand perpendicular to ground.   Rotate entire arm so palm is up (backswing).  Then rotate entire arm so palm is down (downswing).  The front arm rotates.  The rear wrist hinges.

If you take the club too far back (and the sign is the left foot comes off the ground on the backswing), that is part of the reason for casting.   The big 90 degree backswing is probably the biggest farce in golf.   Most people don't have to mobility to do this and over turn the hips.

I'm sorry I have no idea what you just said. Could you please explain the drill

You also need to feel the club so you don't cast it.  Short of being an under 30 year gym rat, most of us are in trouble if we try to replicate Phil by getting the club past parallel (to the ground) on the backswing.  I think that's what you mean by over-hinging.

To get the feel, only take the club back to where your arms are only parallel to the ground, and at this point, the club should be about 90 degrees to arms (pointing directly upright).  Now start rotating your hips to where you are pulling your arms down with your hip rotation.  When you arms are now closing in on directly downward, the club should still be 90 degrees to your arms.  You can then rotate your wrists so the club unhinges through the ball as your arms are moving ahead of the ball.  As you complete your hip rotation towards the target, as your arms are now parallel to the ground (in front of you), your wrists should now have the club again at 90 degrees to the arms/ground. If you catch Martin Hall on the Golf Channel - he refers to this as getting in the 7 position - your left arm should form a seven with your shoulders, and maintain the 7 when your shoulders are square with the ball on the downswing.

For the purpose of the drill, only increase speed, do not increase the backswing past this 50% swing.  You are teaching your muscles how to hold the lag.  It is too easy to backslide if you try to increase the backswing.  The biggest speed multiplier is not getting your shoulder turn to 90 degrees to the target but releasing the lag with the swing through the ball.  Better to build confidence with a 60-75 degree shoulder turn than repeat bad habits trying to squeeze out just a little more turn.  ...Once you get that down, and you can turn back further and stil start your forward rotation with your hips and legs before your arms, go for it.

The rest of us trying to squeeze more turn end up starting with our arms and not the torso.  Over-swinging pretty much guarentees casting.

Hold your left arm at shoulder height like shaking hands.    Rotate your entire arm at shoulder height so the palm is pointing straight down - that is the motion your arm makes on the backswing.   Now rotate your entire arm so the palm is pointing up - this is the motion of your down swing and followthrough.    Your wrist and your arm rotate as one piece.

Go to www.swingsurgeon.com for some good tips.  This is the Don Trahan "in da mitt and tru da tree" swing.   His thing is imagine hitting the catcher's mitt on the takeaway and swinging up into a tree on the followthrough.  DT is one of the biggest opponents of the rotational golf swing and the big 90 degree backswing.

Also, Paul Wilson of Revolution Golf has a series of anti-slice videos.  The reason people come over the top is they try to swing too hard.

Both of these guys have a thing in common: quiet lower body on the backswing with minimal weight shift and active lower body on the downswing.  They promote a more compact backswing (like Stack N Tilt).

You also have check points in your swing.  When your club is at waist height on the backswing it is perpendicular to the ground and still on the target line.  When you are at waist height on the follow through, the clubhead is on the target line and perpendicular to the ground.    

I received a nice tip from a teaching pro at allexperts.com (Eddie Kilthau).  It is called "palm up palm down drill.

For a rightie, hold your left hand at shoulder level with hand perpendicular to ground.   Rotate entire arm so palm is up (backswing).  Then rotate entire arm so palm is down (downswing).  The front arm rotates.  The rear wrist hinges.

If you take the club too far back (and the sign is the left foot comes off the ground on the backswing), that is part of the reason for casting.   The big 90 degree backswing is probably the biggest farce in golf.   Most people don't have to mobility to do this and over turn the hips.

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That was my bad - the palm points down on the backswing and up on the downswing.  Also, I watch Martin Hall and the one I like is "shut your face".

But just like Don says, the most you want to take  the club back is so the arm is shoulder height.     The turning of the hips and lifting the back foot is what starts the downswing.   You keep your wrists set until about the time they pass your back leg and then you rotate to square the club - on the downswing, the upper body is only along for the ride - the lower body does the work.

LOL!!!!!!!!!!!!!!  Gosh, that hurts to laugh that long.

I'm 63 and gave up slow pitch softball 3 years ago to play golf with kids my own age.  I taught myself how to swing a used $5 5-iron 50 years ago, so I perfected about every bad habit in the book over 47 years of occassional play.  I've gotten advice from multiple sources that all say the same thing.  it took 2 years to stop trying to over-rotate and achieving a reverse tilt (turning until I load my weight at the back of the swing on my forward foot).  Once my LPGA got that through my head, we are now beating me to keep my lead arm straight (the proverbial chicken wing) and holding lag down as mentioned.  Now that the snow has finally melted in my back yard, I'll add Hank Haney's advise to take a 100 swings a day - even if you never hit a ball, to train muscles to stay in the 7 (in my case backwards 7 since I'm LH) and release through the ball.  I have added a ton of launch and 10-15 yards with each club when I do.

If only I had been dumb enought to take lessons and listen when I was 17.  <sigh>

In your case, you may get to rotate like a DJ, but only after you get the mechanics of ball contact straight first.