I second what Joshie said.
I would only breed if both were registered and had good conformation AND TEMPERAMENT as well as complimenting one another.
Personally, I wouldn't breed a horse unless I was a breeding stable or wanted a new foal for myself to train and keep forever.
17 for a healthy horse is perfectly fine breeding age, in my opinion. Especially with a vet OK.
But before I say 'yes' or 'no' I'd need more info. Just because a stallion is available and cheap (or free) doesn't mean you should necessarily breed.