A basic level of fitness is required for all those heading outdoors. But for all those yet to begin their adventures, it's not the climb-up-and-down-a- mountain-in-a-few-hours fitness that is required to complete your first trek.
Running is a test of fitness. Trekking is not. Everyone can trek.
Point here is, be in the outdoors if you simply want to be in the outdoors. Make a start, however difficult it may seem at first. Don't let your own perceived lack of fitness stop you. The only thing that can be a problem is your willpower. Your heart will pound heavily and seem to thump straight out of your chest at times. You will get there in the end though, if your heart truly desires the experience and your willpower is sky high.