These are certainly not bad at all, but if you're pushing yourself to improve, here are my thoughts.
1) As was said by others, don't sit him so close to a background. The 2nd shot was done well in this regard.
2) Try shooting between 100 mm - 130 mm. You'll find that his nose won't be so pronounced and he'll probably look a little more pleasing. Don't go all the way to 200 mm or he'll look flat.
3) Try and get some light on the back of his head/shoulders. The easy way is to have the sun do that and then reflect into his face from the sun, but that's just one way of many to do it. (Also, you may not want the sunny look so you'll want a more subtle light. But find something, whatever it is.)
4) When you do a face with one side darker than the other (like #3) make the lighter side the side of the face that's away from the camera. So in that shot he's showing more of his left cheek...his right cheek should be the brighter one in that shot. (Or, easier than moving the lighting, have him turn his head and switch the way he's facing.)
5) You can help glasses reflection by taking the back of the wires over his ears and pushing them UP about a half inch. Be careful not to go so far that they look weird, but just a little movement can help a lot by changing the angle of the lenses.
6) Run a large, feathered 'sharpen' tool over his eyes. Just a little bit. You'll be amazed at how much a slightly sharpened eyeball can really pull you into a photo as a viewer.
But I'm getting very nit-picky there, just because you asked! These photos are already quite good and I bet the subject was thrilled with them. That's your first responsibility so feel good about that! But yeah, nothing wrong with wanting to push yourself past that level. You're doing great already.
