Join Date: May 2009
Location: Winnipeg, Manitoba, Canada
Regardless of size, all horses joints are fused by age 3. Period. After age 3, it's the spine that is concerning, and doesn't fully fuse until a horse is at least 6 years old - and you can tack on a few years if the horse is big.
There's no reason why a 4-5 year old horse can't be started lightly with poles and crossrails. I personally wouldn't be jumping courses until they were 5-6 years old and saving the 2'0"+ stuff for that age, but anytime after 4 is a good place to START. I'd save the heavy stuff until a little older.
I hope God tells her to smash her computer with a sledgehammer.