Faster club head speed relates to lever action around a number of fulcra.

The feet provide the first fulcrum on which the lever of the legs/lower body turn. This must be stable with very little lateral movement. When this turn on the downswing has gone as far as possible, the fulrcum for the body rotation is the inner left foot. The central body provides another fulcrum on which the lever of the upper body rotates. The left shoulder provides another fulcrum on which the lever of the left arm swings and the wrists provide another fulcrum on which the lever of the club swings. All of these must rotate in unison. Club head speed then relates to the amount of lag by the club head in relation to the hands coming into the central 'impact area' and the momentum set up by the body in its rotation. If the hands are close to the centre as the body has rotated through the wrists 'unhinge' automatically and the later this happens the faster the clubhead speed. Keeping control and club head speed is related to timing and remaining 'behind' the centre until the club head has travelled about 40 degrees beyond impact. The maximum accelaration for the best golfers actually occurs past the ball. Unless the clubhead is square on impact, no amount of speed will be useful Witness Ernie's drives in the PGA.

Hope this is not too technical, but it is accurate. Any attempt to hit the ball with the hands and arms is counterproductive to the relaxation needed to let the levers work in unison.

A flexible larger person with perfect timing will hit the ball further than a smaller flexible person with perfect timing but the larger person tends to want to use their 'bulk' and muscles more, which will result in slower clubhead speed.