Well, I am 13 and have always been into biking but never got serious until now. I just took a 6 mile bike ride that was mostly uphill and I completed it in 40 minutes, which I thought was pretty good, but I was gonna die after of it. I have no idea on how to make a training plan. I really just want to work on cardio because I'm defenitely having problems on hills. Any help would be appreciated. Thanks.