Run 3x week. Alternate speed vs. endurance. Every other run I do 2 miles as fast as I can sustain. In between I run 40 minutes and see how far I can get. I had to work up to this; I will work forward from it. Due to my finally finding a fix for a chronic leg muscle problem, I'm getting in better running shape than I have ever been in.
Hike in hills or do elliptical machine at gym on other 3 days. One day, rest.
Once a week - leg strength/endurance/flexibility workout:
In a basketball gym, 3 complete rounds of the following.
Reverse axe chops with medicine ball, 8-10 reps per side.
Walking lunges holding arms outstretched, with medicine ball, 10 reps per side.
Perpendicular walking lunges, rear foot at 90 degrees, front foot forward, arms same as above, 5 reps, switch sides, for total of 10 per side.
Walking side squats, feet parallel, arms in front of torso, torso over forward leg, 5 reps, switch sides, for total of 10 per side.
Step up to knee raises, 10 per side, as fast as possible, alternating sides, on plyo box. Go to a higher box when it gets "easy."
Rest, drink water, repeat.
Do that for a while, and you will find yourself able to hike and climb for a lot longer.