But could use some post processing.

The first image as an example, needs to be white balanced in curves. Select white point on the handle bars post between the handle bars and tyre, and use the black point on his T-Shirt. Adjust the brightness and contrast a little, bumping up the contrast and then do an USM 100%, 0.5 and 1 and see the difference, especially in the trees and rocks.

The person behind the bike down the track a bit is a bit of a distraction as well, maybe less DOF next time and more forcus on the main subject a bit more. Pre focus manually on the point you want to take the image at and try that.

Still not bad with a new camera and using kit lenses as well.