My girlie (10 1/2) can ride him without a saddle or bit. We've had him since July and it's really neat to see how he's grown. His rear end is getting big. He had a line like a comma that you could see from the rear view. That's filling in nicely. He was an arena horse and had been stalled but he's been running around in the the dry lot and pasture since we've had him.
So, to me, a good trail horse has decent conformation and a good attitude.