As I have played, I generally take the sons of Generals into battle as soon as they come of age and have them take charges into light units for the experience. Once they reach three chevrons, I keep them in a province that has numerous slaves to subdue the small rebellions (usually on their own) to gain the "scarred" trait, command stars, etc. Generally speaking, by the time they're 20 they have at least 3 more stars, and five chevrons. This makes for very powerful early cavalry, usually within 10 to 16 turns.