Head is too wide. Looks at pictures of skulls to see what a head should be shaped like. Head is too big overall, cranium is too small. Maybe move the glasses down a pixel then fix the cranium (shouldn’t be flat, either). All the single pixels you’re adding act as unnecessary noise and not texture. Position of the hand on the left is unnatural. Arm on the right is too long and noodly. Try to implement some real anatomy, if it’s just upper arm/lower arm. Cane doesn’t seem to reach the ground, and should be closer to the body to help support his weight. Skin tones don’t vary enough in value, push the contrast a little more, and throw in some hue shifting. A slight bend in the knees might help since he’s old (though he has a big brown beard like a much younger man)