I would definitely NOT have a 14 year old play on a diamond that has 60 ft. bases. This means that the pitchers mound will be 46 feet. Considering many 12 year olds can pitch at 70+ MPH, which is equivelant to over 90 MPH on a 60 foot mound, many 14year olds can throw 80+ MPH. This will be unhittable on a 46 foot mound. As a hitter, they will potentially hit the ball back at the pitcher too fast for him to react, which is not safe.
My point here is that is 14 year olds playing from these distances is unsafe and unplayable. You may want to check the Little League website for distances for the various age groups. Good Luck.