20% is not too much for a trail ride, unless there is something wrong with the horse.
If someone wants maximum speed or maximum jumping, the the less weight the better. But you don't need to be a 110 lb jockey to trail ride. With tack, I weigh 210. On my 900 lb mare, that is 23%. On my 830 lb gelding, that is 25%. Neither has any problem with my weight. I have ridden my 700ish mustang pony. That is 30%, and he has to noticeably adjust his stride and movement to carry my weight. He can do it - he can gallop with me and not breath hard afterward or show any signs of a sore back, but he is obviously taking shorter strides and compensating for all the weight. But yes, he can handle my weight for a 1-2 hour trail ride. No, he couldn't do much jumping with me...