These are the prerequisits to training in my opinion.
-You need to be able to ride with no hands on the reins and no feet in the stirrups. If you can't do this then you can't isolate your cues from sloppy movement.
-You should have extensive knowledge of horses and how they move and think. If you have only taken lessons on one horse for a year it doesn't matter how well you ride you should not be training horses. If you believe that horses act like the horses in movies like Flicka, Black Beauty and the Black Stallion you WILL get hurt and you will NOT be a good trainer.
-A good trainer will have ridden many different horses. If you have been riding the same horse for the last ten years you don't have as much experience as someone that has ridden 5 different horses a day for the last two years. You learn something from every horse so the more horses you ride the more you learn. Internships/working student positions are priceless for this reason.
-You need good facilities and equipment. If you have a $100 thrift store saddle and bridles hung together with baler twine and duct tape you won't look very competent and be haunted with equipment faliures. You don't need a round pen but you do need an enclosure with decent fences and good footing for the first few rides. You don't need a million dollar barn but a good safe pen is a must.
If you ride well and think that you want to start a colt and if you have the things listed above then you should be sucessful. Failure IS an option and it usually spells disaster for the horse. Make no excuses for yourself or your horse. Don't let your ego or emotions take control. There is no room for ego in good horsemanship. Ask for help BEFORE you get in trouble and take the advice of experienced horseman that can show you the results of thier training program.