Resistance or bodyweight training can probably be started whenever. These things should be somewhat simple and easy to do such as sit-ups, crunches, wall sits, lunges, etc. As the swimmer gets older and perfects his or her strokes, they can do more challenging workouts such as medicine balls, stretch cords, etc. Make sure they are using the proper weight for medicine balls and doing the exercises correctly. You do not want to overwork the kids because it may hurt them in the long run.

Lifting weights should not be started until physical maturity. For girls, this is about freshmen year of high school and junior/senior year for boys. Of course it also depends on a person's physical maturity level. Girls tend to plateau physically at about age 14 as opposed to boys who become stronger until 18-20. Though there is little research that suggest weight lifting stunts your growth, many parents and coaches still believe this is bad and even dangerous. To make sure there are no accidents, make sure the weight program is suitable for the child and that they are doing the exercises correctly with good technique. Do not let them overdo it, because this will cause athletes to have injuries that will plague them throughout their careers.