You should be fine because you are going to need several months of trotting (not cantering) ground poles, cavelettis and cross rails before you start raising the jumps anyway. This isn't because the horse is 4, but because he needs to learn how to use his feet, how to rock back and push off the ground and how to think independently about jumping so that he isn't totally dependent on you to tell him when to leave the ground. Once you have that, you'll be able to start gradually raising the bars, adding in small oxers and cantering jumps pretty quickly. By the time you are there though, your horse probably will be rising 5.
And as others have said, limit jump work to a couple times a week at most, although you can do ground poles anytime because he shouldn't "jump" them - although he might at first :p. Ground poles are nice because they have to pay attention to what they are doing to with their feet without having to stress the legs.
I wouldn't put boots on his legs when you start jumping him. You WANT him to feel the pole when he hits it - that is how part of how he will learn to tuck his legs up. And the "strain" on his legs will be minimal bc the jumps will be low. Once you start moving up and get to 3 feet or more or solid x-country-type jumps, that is when the boots should come out. My instructor doesn't boot her main jumper until the jumps hit near 4 ft.
Last edited by PoohLP; 02-24-2012 at 04:30 PM.