I have a 3 year old filly and I'm going to be training her for jumps soon but I was wondering what age to start. I was planning on starting to train her on poles next year but is 4 to young?

4 isn't too young to start poles, but I wouldn't get on her back any earlier than 3. Also, you should get your vet out there to make sure her knees have closed. I have a five year old that I've just started doing larger jumps with. I started him over ground poles at 3.5, cross rails for a year after he turned four, and this summer I've started doing boxes, trees, fences, tires, etc... But it's not really a specific thing, go at the speed of your horse: you'll know if he has developed mentally enough and your vet can tell you if she is physically able.

I have a coming two year old that is just on groundwork, and will be worked light caveletti at liberty when he turns 2, then broke to ride when he is coming 3. Im going to do a dressage base on him until he is 4.5, then start him on his jump training (small, mind you- just teeny crossrails after cavelleti.)
I dont know if this is correct, seeing as I usually am doing barrel horses, but we shall see how he turns out!!!!
Just make sure he is sturdy enough to handle his workload.

I think it depends on the breed. 3 is way too young for a warmblood but some quarter horses knees are closed by then.
I always x-ray my horses before I start jump training. See if those joints are ready for it.