I would say 17 or so before getting serious about training.
4 Years
Not exactly. Rabbis begin their training after high school.
You have to be at least 18 years of age to begin basic training with the Navy, you also have to be at least 18 years of age to enlist into the Navy.
they like to start kids in junior high on weight training for football.
Samurai typically began their training at a young age, around 5 or 6 years old.
See related answer below.
A horse needs to be mature. Generally training begins at age 4.
At 7 years old
The average age a child can begin using scissors is suggested to be age two. At age two a child needs to learn how to build up muscles in the palm of his/her hand and start using eye/hand coordination.
As long as they can wield and handle a katana (Japanese sword), they can begin their training to be a samurai. But many boys begin when they are in the ages of 3 or 4
Between age 11 and 13, depending on her weight.
Royal Marines is from the ages 15 and 9 months to apply and then 16 to begin training up to the age of 33. You must also meet height and weight requirements which is something like 5'4 and 65kg.