Many factors can affect the temperament of a horse or pony, including age, breed/genetics, housing, training, and diet. While feeding your pony a more appropriate amount of energy for its size and activity level may certainly help, don't be surprised if it doesn't necessarily change your pony's attitude from hyper to calm. If your pony comes from a line of "hot"-tempered equines, then training and calm and consistent management will play a key role in developing a calmer attitude.
While five years old is considered a mature equine, horses and ponies mature mentally at different rates based on their breeding and experiences. Your pony may need more time, training, and exposure to different situations before he calms down. Some equines seem to always look at the world through young eyes, even as they reach a ripe old age.
If your pony is housed in a stall, then providing at least four to six hours of turnout a day with other equines would provide more exercise and help your pony relax. Try having your pony turned out before you work with him.
Make sure the 30 minutes you exercise your pony incorporates a lot of steady and consistent training. If you are riding your pony, make sure you practice slow steady work at the walk and trot on various circle sizes. In addition, work on transitions and suppling exercises. You may find that you need to increase your training time to achieve the results you want. For more ideas on training techniques, view the video clips in the eXtension article Fundamentals of Horse Training.
If you think that your pony may be dangerous, seek help from a knowledgeable horse person.
