Exercise is generally not going to stunt your growth. Growth is stunted when you damage the growth plates which are located at the end of your bones. Growth plate damage is most often caused by impact in full contact sport in the same way the young athlete would break bones normally.
Lifting weights will not stunt your growth unless the young person is lifting weights well above their capabilities and lifting with terrible form. A young person lifting the correct weights under competent supervision is not going to damage growth plates and stunt their growth.