Across the armed forces, the minimum age allowed for enlistment is 17 (with parental consent) and 18 (without parental consent). The maximum age for enlistment for someone who has never served in the military before varies by branch; for the Army it's 35, for the Navy it's 34, for the Air Force it's 39 and for the Marines it's 28.
The year of the horse means there is leadership associated with this sign this year, so your authority may increase, according to Ng. However, the impulsive behaviour of the horse can lead to recklessness, so stay away from gambling and speculations.
After a horse is one year old, it is no longer a foal, and is a yearling. There are no special age-related terms for young horses older than yearlings. When young horses reach breeding maturity, the terms change: a filly over three (four in horse racing) is called a mare, and a colt over three is called a stallion.