He looks pretty sturdy. I would just go out for a short ride, maybe with a little bit of climbing in it and see how everyone feels and does by the end of it. Also, I think it depends on what type/weight of saddle you are using, cause you will need to add that to your overall total weight that your horse is carrying.
My little arabian is 14.2 and I'm 5'9" and weigh 148lbs. I use a simco barrel racing saddle that weighs hardly anything or I ride him English. You can see pics of him in my thread Need Opinions, sell or lease. Admiral moves around like I'm a fly on his back. Even though I feel like I'm huge and my feet are almost touching the ground, but we look fine together.