Jump training depends on physical maturity and development, not a specific age.
Puppies under 6 months should focus on basic obedience and gentle play, as jumping can stress growing joints. From 6 to 12 months, simple, low jumps can be introduced. Dogs over 1 year are generally mature enough for more complex jumping, but you should always watch for signs of discomfort.
Breed, health, gradual progression, and safety are important. Consult a professional dog trainer to develop a safe and effective plan for your individual dog.