My mom's mare is built similarly (I've attached a picture of her so you can see how she's built). She's in her 20's, and doing perfectly fine. She has arthritis in her shoulder and hips from her old age, but she can still be ridden on the trails and loves it very much. So, for what you want to do, I think he's perfectly suitable.
An important thing to consider are his feet, though... Have you gotten to look at his feet yet?