Plyometric Age Considerations
Many research studies have been for not only plyometric exercise, but other forms of physical activity as well to determine exactly when an individual is "ready" to begin that form of exercise. In regards to plyometrics, there is no specific age or time when an individual is physically prepared to begin such an intense form of exercise, but there are definitely some information that can be shared.
Growing bones have what are known as "epiphyseal plates" (aka growth plates) that fuse together over time with the maturation of human bones. The stress placed on these plates from very high impact exercises such as depth jumps are not recommended for young individuals who still have physical maturation ahead of them, however that does not mean that plyometrics cannot be added to their training.
Let's not forget that very simply or less-strenuous forms of plyometrics such as running, jogging, jumping sports, agility type drills, are all things kids do at "play" as it is, so it is by no means necessary to deem these forms of activity as too stressful for their growing bodies.
Just as with any aged athlete, plyometrics can increase and aide in muscle and bone development as well as increase sport performance as long as the right precautions are taken.
The important thing at any age, but probably more-so as you age, is to listen to your body and only exercise within your limits. There are many benefits that can be gained from plyometric exercise even for someone who is older, but any physical limitations should not be ignored.
For example, someone who has had a history of knee problems/surgery, should especially avoid single-leg exercises. Other precautions to be taken should include only starting out with 1 plyometric session per week, as well as the least amount of recommended ground contacts per session.