megannnn, what breed is your horse?
That is something very important to consider when deciding about jumping a horse at a young age. Certain breeds and types don't mature until much later. I have a 5 1/2 year old draft pony that I won't be doing anything over 18" with until she's 7. Because drafts take longer to mature. And when she does jump it'll only be a few jumps here and there.
My girl might be fully mature now and mostly like will be by the time she's 6, but I prefer to take it slow. It kills me to see people jumping horse 2', 2' 6", 3"+ on what I consider babies.
Having owned a horse with joints in just about every part of his body destroyed by the age of 7 (he came that way, I was a naive buyer at that time)...well, I'm VERY careful.