The whole concept of growth being stunted by weightlifting is a fairy tale that I have been hearing for years. The American Academy of Pediatrics recently changed their policy (PEDIATRICS Vol. 107 No. 6 June 2001, pp. 1470-1472) regarding this topic by stating that "strength training programs do not seem to stunt growth and do not seem to have any long-term detrimental effect on cardiovascular health.
Weight Training Recommendation
I wouldn't recommend that teens lift any weight that he or she can't do in a controlled manner with perfect form for at 10 repetitions until he or she is 18 or so. A weight that the weight lifter can perform with perfect form for 10-15 repetitions will give you excellent muscle building results. Once you reach the age of18, you can introduce heavier weights but never go below 5 repetitions, due to my experience this rep range is not needed for bodybuilding.
When it comes to teens and lifting weights my concern is not the risk of stunting their growth which won't happen with proper training; what should be of most concern is the risk of injuring tendons, ligaments, or joints that are unused to the demands of heavy lifting. These types of injuries will have affects for the rest of one’s life and will only get worse as they age. This is the reason why I emphasize the importance of proper weight selection and perfect exercise form.
Now look at this topic from this standpoint. Lifting weights didn't stunt the growth of Lebron James, Shaquille O'Neal, David Robinson, Charles Barkley and Karl Malone. All these NBA stars started lifting in their early teens and all have gone on to be 6feet 5 inches tall to 7 ft tall. Arnold Schwarzenegger started lifting in his teens and he is over 6 feet tall., Provided that exercise form, proper weight selection and safety are always emphasized, you will not stunt your growth by lifting weights.