Another important thing to consider is if you have the time to support and train an ex race horse. Training an ex race horse let alone a green horse will consume lots of your time. Just something to remember.
I actually bought a green horse when I had been riding for more than a year, and now it's been a year since I bought her. She wasn't an ex race horse, but she was still pretty green at the time. It was definitely tough at first, but my trainer was helping me along the way. It depends on how ready you feel. I definitely had many ups and downs that either made me happy or made me not want to ride because I was stressed out, but that's just part of the process.
I've been riding for 13 years and have only just begun working with greenies. When you decide to go for it depends a lot of how much you would like to be able to do yourself, and how much of it would be done by a trainer. Best of luck!
It doesn't matter how long you've been riding it only matters how much you know. One of my friends has been riding for 8 years and has amounted to nothing but I've been riding for 3 years and retrained to rescues with bucking and bolting issues
It depends on how experienced you are. Personally, I don't think two years of riding would be enough, but some people learn very quickly. If the trainer thinks it would be appropriate then go for it. But first ask yourself things like:
do I have experience with riding extremely green horses.
Do I have experience riding horses who may have tendencies to take off or rush.
Do I have experience riding hot horses.
Will I be able to have the horse engaging their muscles and using their topline so they can develop any muscles that may have been left week from only racing.