How much training experience do you have? Does he tie, bathe, clip, load, etc...?

At six, he should be "reasonably" chilled out, but all horses are different and a 35 yr old can still bronc w/the best if they feel the need,lol.

Why hasn't he been trained? A horse left to their own devices for that long, depending on what type of human interaction they've had, sometimes can be a right hand full when it finally comes to training.

Was he used as a halter horse? I am not a Quarter Horse girl, but I have a good friend that trains reiners and he said "Halter" Quarters aren't built to be ridden anymore due to various conformation issues.

The person that owns him, is this a breeder?