I think that hiking and backpacking is a great activity for people who have a little extra weight, since you can hike really slow and take a lot of breaks if you need to. I'm a size 16-18 and can cover over ten miles on a good day. I do a lot of exercises to strengthen my legs, like squats and stairs, and those help to support the rest of my weight. The best advice I can give is that you should not compare yourself to anyother hiker, even ones who are the same weight as you. Hike at your own pace and have a great time.