At 16 what worked great for me was a couple of hill sessions a week.
On Tuesdays we ran 20 x a hill loop where the hill had a lesser sloped portion of 100m and a steep portion the last 50m to the top. We accelerated at the base of the hill and the last 50m to the top were very fast. We concentrated on a free wheeling fast recovery down the back part of the loop.
On Thursdays we ran 4 x a loop that included the Tuesday hill, a sand hill, and a long drag 400m hill. We ran this at about 6 minutes/mile pace with speeding up on the hills, recovering downhill. The loop was about a mile long +/-