When you turn 4 years old, you are now able to breed with your opposite gender. They key is to get a friend who wants to join, then breed with your opposite gender, so they can join and be your foal. All you have to do is wonder with your herd, if you find a player who you like, (opposite gender) then ask them if theywant to produce a foal, if they say yes, go off and find a person who wants to play as a foal. Breed and tell the person they can join. The foal must stay with the mother at all times until the age of 2.