I think NinaS hit it on the nose. The most noticeable thing in all the images is the busy backgrounds. You were able to mute it a bit in the first image with the larger distance to help the depth of field but try to isolate him on a more solid background. If its limiting, as an area like that might be, sacrifice your angle for a better background. Although it is better to be at eye level, if you shoot downward a bit with a wide aperture you can use a green grassy field as a nice solid backdrop that doesnt subract from your subject. Good job though, keep it up!