There is some variation as to how fast a golf ball travels for an average player which largely depends on the golf club.
For instance, with a three-wood golf club, you can reach a clubhead rotation speed of 94 and a ball speed of 137 feet per second. With a four-iron, you can expect the clubhead rotation speed to be around 83 resulting in a ball speed of 121 feet per second.
For a seven-iron golf club, the clubhead rotation speed is even further reduced to 79 while the ball speed should be around 109 feet per second.
The maximum velocity for a golf ball should be around 250 feet per second or around 170 miles per hour. There is also an average speed for a golf ball hit by a tour pro which is around 180 miles per hour.